Cities change, of course, but few so dramatically as Pittsburgh. For a place that just a few decades ago had an economy that virtually hinged on the steel industry, Pittsburgh methodically has shifted gears, changed directions and totally altered its economy as well as its skyline.

In the old "Steel City," where the smokestacks of mills once dominated the sky above hills and valleys formed by the Allegheny, Monongahela and Ohio Rivers that converge here, steel, glass and marble-sheathed towers now convey Pittsburgh's diverse corporate and high-tech image.Visitors who arrive here from Greater Pittsburgh Airport, or via the southern suburbs, drive through the Ft. Pitt Tunnel beneath Mt. Washington and onto the Ft. Pitt Bridge. They are stunned by the view. The immediate sights, day or night, are a melange of bridges and the dramatic skyline of the Golden Triangle, as Pittsburgh's downtown is known.

Rising beyond the green expanse of what is now State Point Park, the site of historic Ft. Pitt and much later a district of derelict buildings, the Golden Triangle's ranks of skyscrapers virtually hit visitors in the face. For first-timers, the reaction is simple: Wow!

Even for those who once lived here, me included, the Thomas Wolfe statement - "You can't go home again" - doesn't quite hold. You can go home again. It's just that you might have difficulty recognizing what once was the less-than-desirable city you left behind.

Renaissance is the term used by city officials to describe Pittsburgh's regeneration phases. Renaissance I began about 1950, and II, in the 1970s. Renaissance is the appropriate word because the city is enjoying a rebirth, a new vigor. Pittsburgh is a city in transition, and visitors come here from all over the world to witness the change.

Transition has come so swiftly that in 1985, Rand McNally's "Places Rated Almanac" named Pittsburgh "the most liveable city in the nation." Four years later, it still ranked among the top three, behind Seattle and San Francisco. Pittsburgh's topography of rivers and hills topped with trees and homes has carved the city into a patchwork of ethnic neighborhoods that harmoniously live together and enrich the city's character.

Big names in U.S. industrial history made their marks in Pittsburgh - and on the city. Andrew Carnegie forged a fortune in iron and steel. So did industrialist Henry Clay Frick, food processor H.J. Heinz, financier Andrew Mellon and inventor/industrialist George Westinghouse. Those giants and their heirs made billions of dollars here and elsewhere. They became the city's chief benefactors, leaving Pittsburgh with a solid foundation of cultural and educational institutions on which the city has developed and continues to build.

In addition to the socially conscious, philanthropic big names, 12 Fortune 500 companies make their headquarters here - USX, Westinghouse, Alcoa, PPG (Pittsburgh Plate Glass) Industries, H. J. Heinz, Bayer USA, National Steel, Cyclops, Allegheny Ludlum, Aristech Chemical, Allegheny International and H. H. Robertson. They, too, contribute to the city's culture. What makes that list remarkable is that Pittsburgh, founded in 1758 and incorporated in 1816, has fewer than 400,000 residents. The regional population is an estimated 2.2 million.

Pittsburgh and its hard-working, blue-collar/white collar population also witnessed a rebirth of its professional sports franchises. The Pittsburgh Steelers, founded by the late Art Rooney, won four National Football League Super Bowls (1975, '76, '79 and '80), and the Pirates, three baseball World Series championships (1960, 1971 and 1979). Only the scrappy Penguins of the National Hockey League have come up empty. Today the Pirates are battling the New York Mets for the East Division championship of the National League. And the Steelers, who made the playoffs last year, are optimistic about the coming season.

Pittsburgh's winning ways have not come easily. The first phase toward regenerating the city was led by Richard King Mellon and the late Mayor David L. Lawrence, a Democratic power who late became governor. Renaissance I, launched about 1950, imposed smoke and flood control measures and developed Point State Park and Gateway Center that adjoins it, Civic Arena, Three Rivers Stadium, 64-story tall Cor-Ten steel USX Tower and Mellon Square.

Renaissance II in the 1970s and '80s, spearheaded by the late Mayor Richard S. Caliguiri, brought the David L. Lawrence Convention Center, the Light Rail Transit and Subway System, Station Square and several skyscrapers, including the 40-story PPG Place, the shining glass and steel towers in a Gothic style. The new buildings live easily with the venerable ones from the early 1900s. The mix leaves the city with a slightly rough texture that connects its industrial past to its future. Both reflect the affluence Pittsburgh enjoyed, even when its skies were smoke-filled.

Today, Pittsburghers point to their unusual new buildings, their esteemed University of Pittsburgh and Carnegie-Mellon University, hospitals that have joined the nation's leading cardiac and organ transplant centers, and a growing performing arts district. And yet, this city which is neither East Coast nor Midwest in feeling still clings to its down-to-earth image and ethnic pride.

Pittsburgh claims a lot of firsts: KDKA, the world's first commercial radio station; WQED, the nation's first public television station; the Cathedral of Learning, a 44-story university skyscraper; the development by Dr. Jonas Salk of the first polio vaccine while he was at the University of Pittsburgh; first successful petroleum refinery in the Western Hemisphere; the game of Bingo about 1920;; the banana split in 1904; indoor ice skating rink in 1894; first professional ice hockey circuit; first World Series night game on Oct. 13, 1971, against Baltimore; the Ferris wheel; the first drive-in auto gas station; McDonald's Big Mac sandwich, introduced in the area in 1961; and a delicacy known as chipped ham, which is sandwiched between two slices of soft white bread.

As a destination, Pittsburgh is not in Chicago's league. But it boasts a first-rate symphony orchestra, ample theater, opera, ballet, art galleries and, of course, year-around sports activities. During the summer Pittsburgh is bustling with its Three Rivers Arts Festival and the recently concluded Three Rivers Regatta.

Besides the gleaming buildings that rose in the 1970s and 1980s and venerable ones from early in this century in the Golden Triangle, Pittsburgh offers visitors an array of quality attractions - Station Square, the old Pittsburgh & Lake Erie Railroad Terminal handsomely restored into a lively complex of restaurants, shops, a Sheraton Hotel and boat rides on the rivers; the Strip District, a run-down wholesale produce market that now draws locals to its retail stores and restaurants; The Carnegie, a combination of Chicago's Art Institute and Field Museum; and the University of Pittsburgh's 42-story Cathedral of Learning, a Gothic wonder that contains 23 authentically styled Nationality Classrooms.

The sights visitors to Pittsburgh are most likely to see over a long weekend or a one-or two-day visit lie mainly within the the Golden Triangle, or on either side of the river - Station Square and Carson Street across the Monongahela on the South Side; Three Rivers Stadium across the Allegheney on the North Side. From any major downtown hotel - the Pittsburgh Hilton and Towers, the Sheraton at Station Square, the landmark Westin William Penn, the Vista International, Hyatt and Ramada - most of the downtown sights are walkable.

But visitors also can use Pittsburgh's free, three-stop downtown subway system, built to ease traffic congestion. Within a couple of minutes, you can get from the USX Center to Gateway Center near Point State Park. An added bonus: Classical music plays in the clean, modern stations. The subway, which opened in 1987, charges 60 cents to cross the Monongahela River to the Station Square entertainment/hotel complex.

Within the confines of the Golden Triangle, visitors can enjoy the new buildings, their soaring lobbies dotted with art and sculpture displays or galleries of boutiques and restaurants. Many of the older buildings reflect the staid elegance of their time. One evening, walking back from the Common Plea Restaurant opposite the Allegheney County Courthouse and Jail, I noticed a lighted castle-like structure atop the Union Trust Building next to the historic William Penn Hotel. Commissioned by Frick, who supplied coke to Carnegie's mills, the building is described as Flemmish Gothic, a style once associated with prosperous commerce. The "castle," it turned out, was not a Frick penthouse, but simply the housing for elevator equipment and a water tank.

On 6th Avenue, a block from the Westin William Penn, Mellon Square and the Alcoa Building, sits soot-blackened Trinity Episcopal Cathedral, built in 1870-72 and looking more like it belongs in Edinburgh than in Pittsburgh, and the First Presbyterian Church (1905), with stained glass by Tiffany. In Trinity's old cemetery, rest some of the city's historic figures.

"The Trinity Church Burying Ground. Pittsburgh's oldest unreconstructed landmark," reads a plaque on the fence. "This whole city block one time held as many as 4,000 graves. An ancient Indian Tumulus burying mound originally occupied part of the site. Subsequently, the French of Ft. Duquesne in 1754 and the British from Ft. Pitt, 1758, along with early Americans who are buried here, prominent persons whose remains are still interred and marked include Red Pole, who at one time was principal chief of the Shawnee Indian Nation, Dr. Nathaniel Bedford, the city's first physician and a founder of the University of Pittsburgh, Gen. William Butler, and Col. James Butler, soldiers of the Revolutionary War and the War of 1812, for whose family Butler County was named, Oliver Ormsby, early Pittsburgher for whom Mt. Oliver was named. ... Relatives of Gen. John Neville, Capt. Nathaniel Irish, a Revolutionary War officer, early settler and one of the founders of Pittsburgh. Many of the names are familiar to most Pittsburghers because streets, areas, islands are named for them."

Opposite the church is the handsome old Duquense Club, dating to 1889, where Pittsburgh's power elite meet to eat.

A block farther, at 6th and Liberty Avenues, rises the 34-story CNG (Consolidated Natural Gas) Tower. The three-year-old building is flanked by two shady sculpture plazas that abut Heinz Hall, formerly the Penn Theater and now the lavish home of the Pittsburgh Symphony Orchestra. A block away, a $42 million restoration job turned the Stanley Theater, another movie palace, into the Benedum Center, home to the Pittsburgh Opera, Ballet Theater, Dance Council and the Civic Light Opera as well as Broadway shows. The two transformed movie houses form the nucleus of a planned cultural district.

Toward Gateway Center on Penn Avenue, the stroller comes to Horne's, along with Kaufmann's, an old, established department store. A marker on the building's exterior is significant: It marks the crest of the March 1936 flood, 46 feet above river level and well over the store's ground floor display windows.

Point State Park, an expanse of green opposite the Hilton Hotel, contains the 1764 Ft. Pitt Blockhouse and Ft. Pitt Museum. The French first established Ft. Duquesne on this site in 1754, but lost it to the British in 1758, the year Pittsburgh was founded.

The park, scene of summer concerts, affords an excellent view of the three rivers, Three Rivers Stadium, Mt. Washington and the Golden Triangle from its tip, where a fountain normally shoots a plume of water 150-feet into the air. From the point, the Ohio River flows nearly 1,000 miles to the southern tip of Illinois where it joins the Mississippi.

During the day, or at night when the downtown empties, there's always action at Station Square, a 10 or 15 minute walk via the Smithfield Street Bridge over the Monongahela on the South Side.

The former P&LE Railroad Station, built in 1901, and the adjacent shed, were beautifully restored in 1978 and now house restaurants, bars and more than 65 shops. The opulent Grand Concourse restaurant, noted for its seafood, occupies the station's old waiting room, with a 60-foot-long stained glass vaulted ceiling 45 feet above the floor. The Gandy Dancer Saloon, part of Grand Concourse, has a popular raw bar and draws a lot of singles.

Steps away are the Sheraton, a popular convention hotel; the Gateway Clipper fleet, which conducts a variety of river cruises; and the Pittsburgh Sports Garden, a new warehouse-like building that feature a one-on-one basketball court, a boxing ring, electronic games, bigger-than-life TV screens, a large bar and a menu that offers everything from pizza and burgers to chili and zucchini rings. Also in the neighborhood are two inclines that climb Mt. Washington, perfect spots for a bird's-eye view of the Triange; and Carson Street, once a rundown strip that serviced the mills and adjoining neighborhoods, now gentrified with antique shops and trendy restaurants and regular stores that still serve the nearby residents.

Another of Pittsburgh's born-again neighborhoods is the Strip District, a 20-minute walk or a short taxi ride from the Westin, Vista, Hyatt and convention center. Still a major wholesale marketplace that services the city with produce and other grocery staples, the Strip slowly entered the retail business.

"As supermarket chains moved out of Pittsburgh to the suburbs and population declined, wholesalers lost business so they started to sell retail, too," said Bernie Benkovitz, president of the Strip Association and owner of Benkovitz Seafoods. Benkovitz, whose family has been in the fish business since 1920, not only sells wholesale and retail, but has a stand-up operation in his store that sells fresh fish sandwiches, chowders and salads. The quick lunch crown ranges from cops and truck drivers to well-dressed lawyers and physicians.

During the week, but especially on Saturdays, throngs of Pittsburghers visit the Strip's eclectic mix of old brick buildings with sidewalk overhangs of corrugated steel and faded signs. They can wander into Fortunes Food & Coffee Co, which carries 55 different blends of coffee. The smells of produce, spices, cheese, flowers, coffee and fill the nostrils, the aromas of a Middle East market in Pittsburgh. But the names are Alioto, Tedesco, La Prima, USA Gourmet, Reyna, Stamoolis, Rubino, Benkovitz, Waldman and Hermanowski.

But, like elsewhere in Pittsburgh, change is coming in the form of Down by the Riverside, referring to the Allegheny, a proposed $50 million development that will include a hotel, floating boardwalk, sports complex, entertainment center, a marina and parking for 5,000 cars.

"The rivers hold the largest potential for tourism in Pittsburgh and really have been underdeveloped for the most part," observed Carol M. Weir, economic development director for the Allegheny Conference on Community Development, a private nonprofit organization. "We have the Three Rivers Arts Festival and the regatta, but as far as a regular use of the rivers for recreation and tourism, there hasn't been that much."

Oakland, about four miles east of the Golden Triangle, looks like its part of a different city. With many impressive buildings, Oakland is Pittsburgh's academic heart, home of the University of Pittsburgh, Carnegie-Mellon University, medical and research centers and the Carnegie, which is simply what the Carnegie Museum is called.

Visitors focus on the Cathedral of Learning, mainly to tour Pitt's 23 Nationality Classrooms, gifts from nationality groups in Allegheny County. Rooms range from Early American to Yugoslav Folk, from Armenian Medieval to Scottish Gentry. Newest additions represent Israel and African American culture.

At the nearby Carnegie, which recently had its old, smoke-blackened facade sandblasted to a gleaming gray, visitors can see the museum's superb dinosaur collection, brilliant gem rooms and a survey of art ranging from French Impressionism to works by western Pennsylvania artists. Two especially convey the Steel City feeling - "The Jones & Laughlin Mill" in 1920 by Johanna K.W. Hailman, and "Around the Mills" by Aaron Gorson.

Oakland was the home of old Forbes Field, where the Pirates and Steelers played in a Wrigley Field-like atmosphere. Sentimental Pittsburghers managed to retain part of the left field wall in Schenley Park and home plate beneath plexiglass in the University of Pittsburgh's Forbes Quadrangle.

One of Oakland's oldest traditions remains the "O," short for Original Hot Dog Shop, a stop for locals and students in need of a dog with everything on it.

Another totally different neighborhood close to Oakland is Shadyside, where Walnut Street has its own upscale boutiques and popular restaurants.

Amazing place, Pittsburgh. It keeps on getting better. A new Carnegie Science Center is rising next to Three Rivers Stadium. A $600 million airport is scheduled to open two miles west of the old one in 1992. New buildings keep sprouting. Slowly, one of America's best-kept secrets is getting discovered. But, from someone who has lived here, it's still a nicer place to visit.

For additional information, contact the Greater Pittsburgh Convention & Visitors Bureau, Four Gateway Center, Pittsburgh, Pa. 15222; phone 412-281-7711 or 800-821-1888. In Pennsylvania, 800-255-0855.