Tonight marks the 20th annual "Messiah Sing-Along" at the Kennedy Center, one of the hottest tickets in town, right up there with the Gridiron Club's annual dinner, Redskins games and the Kennedy Center Honors.

This year, free tickets for the sing-along were distributed on the morning of Dec. 1, and by midnight the ticket vigil had already started on the Kennedy Center's cold marble terrace.

This process of waiting in line for sing-along tickets has taken on a life of its own. Many of the same people come back year after year, and a certain camaraderie has developed as they plan their strategies to get tickets and survive the winter night.

Some arrive with lawn chairs, picnic baskets, thermos jugs full of coffee or soup, blankets and sleeping bags. Others bring candelabra and crystal stemware -- perfect for sipping orange juice while looking out over the Potomac from the terrace at dawn. People of all ages come -- including tiny children.

A reliable source at the Kennedy Center reports that one gentleman celebrates the ticket ritual every year by giving a dinner party at his home and then taking his guests to the Kennedy Center by limousine at midnight to join the ticket line. Some people use their time in line to write Christmas cards. Others play backgammon or UNO.

The Park Service reports that a rush of ticket-seekers arrives about 4 a.m., and the line begins to snake around the building. Another crowd comes at about 6. Normally, the Kennedy Center opens at 10 a.m., but on sing-along ticket day, the doors open between 8 a.m. and 9 a.m. so that staff members can give out ticket vouchers, two per person. When the 2,700 seats of the Concert Hall are exhausted, people without vouchers are advised to leave. But many don't.

A baritone who lives in Foggy Bottom says he saw notices this year saying tickets would be distributed at 10 a.m. The notice also advised ticket seekers to come early. He went at 9:45, assuming that was time enough, and found to his astonishment that people who arrived after 8:15 had been cut off.

"People were still hanging around hoping to find something," he says. "They begged and begged. I guess people could scalp the tickets. I know I'd pay."

People lucky enough to get vouchers could use the center's facilities, enjoy the U.S. Army Band Brass Ensemble playing on the steps of the Opera House, buy "Messiah" scores and watch performers in costume who had come to entertain them. The new chairman of the Kennedy Center, James Wolfensohn, welcomed them this year and handed out schedules for the center's holiday events. Finally, voucher numbers were called and tickets distributed.

Paul Hill, director of the Paul Hill Chorale, initiated the tradition of the sing-along and remains its chief conductor and coach. He brings in his chorus for the event every year and makes a special effort to have other area conductors -- from churches, the military, universities and other choral groups -- join him on the podium. This year Martin Feinstein, general director of the Washington Opera, will, as usual, lead the "Hallelujah Chorus."

"All the conductors are just such a kick," says a Washington singer. "You see their different styles and enjoy their humor."

When the big night finally arrives, the Kennedy Center's Hall of States is full of people camping again -- this time inside -- in hopes of picking up returned tickets. Picnics and pizza boxes are in evidence. By the time the "Messiah Sing-Along" gets underway, the Concert Hall is full of choristers, while hundreds more fill the Grand Foyer, singing along as they follow the conductors on special monitors.

Carol Petrie of Silver Spring attended her first sing-along four years ago. "People think 'Messiah' won't be hard because it's familiar," she says. "But it's a fairly complicated piece of music with all those runs and tricky rhythms. And the sopranos are high up there all night."

After that first experience, Petrie began voice lessons with Annette Poulard, last year's soprano soloist, in order to learn the work. "I decided that if I'm going to lift my voice, I've got to know the music; it would be more fun that way," Petrie says. "My goal was to know the notes and have no sore throat at the end of the evening."

Why does this event have such spectacular drawing power?

A cynic would say the price is right.

A musician would say Handel's music is glorious.

But there is something more.

Mary Graham of Washington, whose voice delights those who stand in the ranks near her, refers to the "exhilarating experience" of making music. "The emotional release of music and the sheer sound make it so wonderful," she says.

Petrie notes that participation in the "Messiah Sing-Along" crosses cultural and age barriers. She tells of a little girl of about 4 who gently repeated "Hallelujah! Hallelujah! Hallelujah!" throughout the "Hallelujah Chorus" last year but neglected to stay silent during the rests prior to the final "Hallelujah!" Realizing her error, she clasped her hand over her mouth and said, "Oh, oh!" Everyone nearby smiled.

"Music is a balm," Petrie says. "And here you have all these voices raised in harmony. It is something spiritual. There's just no way to walk out of a 'Messiah Sing-Along' without feeling great." -- Louise Remmey has been a Washington journalist since 1960.