With block after block of towering, glass-and-steel skyscrapers, downtown Denver looks as if it should host a big-time rush hour.

Yet, at 5:25 on a mid-week summer afternoon, the dearth of traffic - both pedestrian and automobile - is almost eerie for a city of 500,000 and a metro area population of 1.88 million.At the time of day when downtown areas of Chicago, New York and Washington are experiencing near-gridlock conditions, a person can drive in comparative comfort through the heart of Denver's business district.

But out-of-towners should not be too quick to credit city planners with devising ways to spare Denverites the aggravations of big-city life. In fact, civic leaders here no doubt would sleep more soundly if there were a little more congestion downtown - a tad less elbow room - or at least enough activity to signal a healthier economy.

After more than a decade of virtually unsolicited prosperity, Denver, the economic hub of the Rocky Mountain states, has fallen on hard times largely because of setbacks in the mining, oil and gas industries. Along with, and contributing to, the economic woes, Colorado's once sizable and steady influx of well-heeled newcomers has trickled to a halt.

State and local leaders, who 10 years ago were wondering if their environmentally delicate region could handle growth at such a rapid pace, suddenly are faced with the unfamiliar challenge of attracting new businesses to take up the slack.

But there are signs that Denver at least is back on the right track, the most significant indicator being the recent referendum approving plans to build a $3 billion municipal airport to replace 59-year-old Stapleton International. When completed in the mid-1990s, the new facility will be the largest airport in the world in area - and the second busiest in the United States by the year 2000 - and could, leaders here hope, make Denver a key port-of-call in international commerce.

"We can't talk about the positive things happening around here without highlighting how important that airport is," says Robert P. Ortlip, the city's economic development specialist. "I'd venture to say it is the single most important economic generator for the future prospects of this area. This airport will give us the opportunity to market the area on a more national and international basis."

"We're about halfway between the Orient and Europe, and we're not much farther from the Orient than is the West Coast, if you look at the polar (air) routes," adds George S. Dibble Jr., president of the Colorado Association of Commerce and Industry. "With a new, international mega-airport, we could really position ourselves as a trade center."

The airport also will have an immediate impact on local employment, providing direct jobs for about 34,000 persons and generating thousands of additional jobs throughout the area, Ortlip says.

Another positive step for the area's economy is the commitment by Gov. Roy Romer and the state legislature to declare Colorado "open for business." Since he took office in January 1987, Romer has played catch-up by creating state agencies to lure major employers and foster the establishment of small businesses, programs that have been in effect for years in many industrial states.

The Romer administration's biggest coup so far was Colorado's victory in a 14-state battle for US WEST's planned $50 million high-tech research center, which will be built at the University of Colorado's Research Park in Boulder, considered part of the Denver metro area. The facility will begin with a 450-person staff, but eventually will employ up to 1,500 persons.

Also in the past year, 50 companies have announced plans to move to Colorado or expand existing operations that will add more than 12,000 new jobs, reports Blueprint for Colorado, a Denver-based partnership between the public and private sectors aimed at co-ordinating economic development strategies.

Dibble also points out that even though Denver was rocked by the collapse of the energy industry, it wasn't hit as hard as cities such as Houston, Dallas and Oklahoma City, which had virtually all their eggs in the energy basket.

Colorado's reliable tourism and travel industry, especially, played an important role in helping Denver make it through the darkest years. The Colorado Board of Tourism estimates visitors pump more than $5 billion into the state's economy each year, much of it in the Denver area. The board projects visitor spending to surpass $6 billion by 1989.

But despite whatever growth occurs down the road, it is unlikely Denver ever again will experience anything like the boom years of the 1970s, when all the Mile High City had to do was nestle invitingly near the foothills of the Rockies and wait for the money to roll in.

"For Colorado and particularly the (Denver) metro area, in the '70s and early '80s it was a no-brainer for economic growth," recalls Dibble, also the former chairman of the state oil and gas association.

"The oil industry was flourishing, and people were flocking in here with money to invest in energy," he said. "We saw an influx of so-called high-tech industries, like bio-technology, micro-electronics, you name it. Our concern was how do we manage our growth, not how do we stimulate growth. Well, that came to kind of a screeching halt."

But Denver in the late 1980s is a city too big for its economic britches. It's overbuilt. Like the Rockies that define the horizon 25 miles to the west, the city's modern skyscrapers are impressive as scenery, but, as Dibble and Ortlip admit, underused for their intended purpose as centerpieces for a thriving business community.

The vacancy rate in downtown office buildings is a whopping 27 percent at a time when 10 percent is considered a safe cushion in other cities, a situation that explains the city's mild rush hours.

The 6.5 million-square-foot office space surplus is the result of a construction binge spawned by the boom years, when developers, eyeing a downtown vacancy rate of less than 5 percent in 1980, attempted to keep pace with expected continued growth by adding 14 million square feet between 1980 and 1985.

"Our demand for office space to serve these growing, burgeoning industries was just incredible," says Ortlip. "We were building at a rate that was being absorbed, but we kept on building after the economy turned (down). Denver has essentially been redlined by national lenders because of our overbuilt situation."

As Denver's new skyline grew, the bottom fell out of the domestic energy business when a worldwide oil glut caused prices to collapse by 50 percent between 1985 and 1986. A corresponding international recession prompted a drastic reduction in mining operations everywhere. Slowdowns in both industries, as well as ripple effects from the national farm crisis and a cautious retrenchment in the high-tech sector, had a sudden dampening effect on Denver's economy.

"When you're going that fast and you hit the brakes that suddenly, it's a real shock," says Lucy Black Creighton, vice president and economist at First Interstate Bank of Denver.

During the slump, Denver's unemployment rate went from 4.7 percent in 1984 to 7.1 percent in 1987, with the state unemployment rates slightly higher for the same years. As unemployment climbed, net migration into Colorado declined for the first time in more than a decade.

From 1970 to 1982, the state's population grew by an average of 3 percent a year, much of it due to an average net migration of 43,000 newcomers annually, many of them well-educated young adults lured by economic opportunities in the Denver area and its proximity to the pristine Rockies.

But by 1983, net migration had dropped to 24,000, and by 1985 it was down to 4,000. Finally, by 1986 and 1987, the migration trend had flipped-flopped, with an estimated 3,000 to 4,000 more people leaving the state than arriving. The annual growth rate now is down to about 1 percent, entirely the result of the birth rate out-pacing the death rate.

Economist Creighton says the trend likely will reverse itself again if the region's economy shows continued improvement - the unemployment already has dropped to about 6.5 percent - but she does not expect to see net migration surpass 15,000 to 20,000 persons a year.

But experts here say a slower, steadier growth pattern is just what Denver and the state need to break out of the boom-or-bust cycle that has characterized the local economy in recent years. It will also give planners time to address certain serious, chronic problems, such as the metro area's infamous "brown cloud" of air pollution and its growing demand for water, before such matters become full-blown crises.

"Things are starting to build, but they're building in a logical, sane way, as opposed to before, which was kind of insane," Dibble says. "The silver lining to any kind of slowdown is that it made us in the business community stop and examine what we're doing and decide if it's going to be good for the state in the long run.

"Are we doing some things now that will help rebuild the economy, or are we just sitting on our laurels, like we did 15 years ago? It kind of got our attention."