Thousands stand in the ruins, stare up at the sky and wait.

Will they be early? Will they be late? Will they show up at all?Suddenly, somebody sees a black speck in the distance. Then more specks. The sky grows dark with birds. . . right on schedule, they begin to flutter in. A cheer goes up. Paul Arbisbo, who's 90-plus, rings the bells. And at Mission Control, where banks of telephones have been installed, the joyous word goes out: The swallows have come back to Capistrano!

Some call it a mere coincidence. Some call it a miracle.

Brian McInerney, director of the Visitors Center at Mission San Juan Capistrano, isn't sure what to call the remarkable incident that takes place each St. Joseph's Day, March 19. Probably, he says, the return of the swallows is just one of nature's laws manifesting itself - the birds' migratory instinct. Still, you wonder how the tiny creatures can know just when to make the journey; how they can navigate thousands of miles from Argentina without a compass and how they can arrive so faithfully on the same day each spring.

"I've seen cynics stand and watch - totally amazed," McInerney says. "Whether you believe in miracles or not, it's an impressive experience and a very symbolic one. Most people see the return of the swallows as a sign of hope: spring has arrived; life has renewed itself; the cycle goes on.

"I see it as an omen. If a great many birds return, all's right with the world. If the numbers are sparse, watch out! History has proven that man can learn from his fellow creatures if he will only pay attention. How the birds act can tell us volumes about our environment."

According to mission records, McInerney continues, few birds returned in the '60s and many of the babies that hatched were deformed. Pesticides, it turned out, were wreaking havoc with wildlife on the migratory route and nature was issuing a warning.

During recent years, thank goodness, such sobering incidents haven't taken place. Last spring, in fact, there was cause for real celebration. A record number of swallows filled the sky. It was a very good year. But even in bad times, the birds have always made a showing.

Little splinter groups may arrive a bit early or a bit late. McInerney's quick to point that out. And, yes, there even have been instances when the big migration was delayed. In 1935 - he believes that was the year - terrible storms on the 6,000-mile route from Argentina slowed the birds down. But just as people at the mission were about to give up, dozens of the little creatures swooped down. The bells rang out!

Why do the birds, identified by biologists as square-tailed cliff swallows, brave storms and hardships to make the journey? Why do they seem to prefer the mission above all other nesting sites?

Townspeople have an answer for that - a little legend they like to tell visitors.

The swallows, they say, didn't always live at the mission. Many of their original nests were located under the eaves at a local inn. Here they chattered away and sailed in and out looking after their young until the innkeeper couldn't stand all the chirping any longer. In a fit of rage, he destroyed their nests and drove them from their homes. One of the kindly mission fathers happened to be passing by and his heart was touched by the poor birds' plight.

"Come swallows," said the padre. "Come to the mission and we will give you shelter. There is room enough for all."

The grateful swallows took sanctuary in the warmth and safety of the church and, from that moment on, became as much a part of the mission as its historic bells.

"Without the swallows it just wouldn't be Capistrano," says McInerney. "You'd have the colorful history, of course, but it just wouldn't be the same."

The legend first came to general attention back in 1928. Radio was very important then and very competitive, says the head of the mission's visitors center. At NBC they were looking for interesting things to broadcast that would get public attention and one of the Catholic fathers suggested the return of the swallows. It was perfect! Broadcasters moved into the mission on St. Joseph's Day, set up their equipment and described the swallows' arrival in vivid detail.

Then in 1939, Leon Rene wrote "When the Swallows Come Back to Capistrano." The popular ballad put the Southern California community on the map and thousands of people all across the nation started humming the tune and making the pilgrimage each spring. Last year on St. Joseph's Day, over 20,000 visitors came to town, statistics at the Chamber of Commerce show.

"The swallows have been good for our city's image, tourism and economy," says McInerney. "Around here the birds are treated like kings."

On March 18, the Swallows Day Parade, the largest non-motorized parade in the West, winds its way through the historic districts.

After the parade, visitors often wander along Los Rios Street, the oldest occupied street in California, where historic adobes, some dating from the 1700s, can be found. The O'Neill Museum, home of the Capistrano Historical Society is there, located in a Victorian residence - Pryor House. An interesting railway station's close by. You can walk over to El Camino Real, the route the Franciscan friars took as they traveled the coast establishing missions. And there are scads of shops where you can buy antiques and souvenirs.

Of course, it's the mission that's the major tourist attraction in the city. And although March 19th is a great day to visit - mariachi bands play on the grounds, there's dancing, Indian arts and crafts demonstrations take place and excitement's in the air - the historical site's open every day of the year. Hours are 7:30 a.m. to 5 p.m., admission charge is minimal and a portion of the funds goes toward the preservation of old mission grounds and buildings.

Mission San Juan Capistrano is over 200 years old and was established by Father Junipero Serra. It's the seventh in the chain of 21 California missions founded by the Franciscan friars of the Roman Catholic Church. The missions played a powerful role in the Spanish settlement of California and dot the coast. (The line of missions stretches from San Diego de Alcala, 1769, to San Francisco Solano, built in 1823.)

Capistrano joined the mission chain in 1776 and, like its sister structures, served as a center for converting the Indians to Christianity and teaching them farming, weaving and other skills.

From the beginning, the padres called it the Jewel of the Missions. It was clearly meant to be the crowning achievement of the movement and to boast the most beautiful church.

Construction on Great Stone Church began in 1797 and continued for nine years as stones were laboriously quarried from Mission Viejo, six miles away. Built in the shape of a cross, the magnificent church - one of the largest in North America - was dedicated in 1806. In 1812, as the faithful knelt to pray, an earthquake of tremendous magnitude - seismologists still come to the site to try and determine how strong it was - hit Capistrano. The mighty structure, save for the area close to the altar, collapsed and almost everyone inside was killed.

Today all that remains are a graveyard, ivy-covered ruins and a silent, cave-like shell.

"The swallows love it; to them it's like a cliff and they nest there," McInerney explains. "Perhaps it was the Great Stone Church that attracted them to the mission in the first place. Anyway, over the years they've managed to take the tragedy away from this scene and and fill it with life and hope."

A new church based on the original has been built not far away. And, according to the director of the visitors center, it has been designed to withstand earthquakes of 9.0 magnitude so that such a disaster will never happen again.

Still intact at Mission San Juan Capistrano is Father Serra's chapel, built in 1777 - the oldest building in California where the famous padre gave mass. The beautiful altar in the church is made of cherry wood with gold overlay. It is more than 300 years old and is from Barcelona, Spain.

Adjacent to the church is a tiny chapel - St. Peregrine's, the patron saint of cancer sufferers. Each day, according to McInerney, people with the disease or with loved ones who are afflicted, come to the mission to light candles and pray.

On the mission grounds that cover about 10 acres visitors also will find interesting museum rooms featuring early California artifacts and dioramas relating to Native Americans. There are soldiers' barracks (each group of missionaries was assigned a small troop of foot soldiers); a padres' kitchen; metal furnaces where keys and such were made; tanning vats where Indians tanned hides to make leather goods; tallow ovens for rendering the fat that was used in the manufacturing of soap, candles and the like.

Beautiful fountains are on the grounds, too, as well as friendly pigeons that will eat out of your hand.

McInerney points out that there's an ongoing program at the mission to improve the grounds and make sure only vegetation native to the area is represented. A constant preservation program in the Serra chapel and other buildings also is going on, as are archaeological digs.

Of course, the primary tourist attraction will always be the swallows. And if you missed seeing them arrive, you might think about heading for San Juan Capistrano on the day they leave, Oct. 23, St. John's Day. (St. John Capistran, who lived in about 1386, is the Catholic Saint for whom San Juan Capistrano is named.)

There will be celebrating - and a few tears - as the town observes "Adios de las Golonrinas." And then as the flocks of swallows fade from view, on their way to Argentina, everyone will start looking forward to another spring.