They were brunching on bagels, brioches and Bloody Marys, champagne, quiche Lorraine and eggs every which way.

They were doing it in crowded Georgetown bars, noisy neighborhood pubs, under crystal chandieliers in downtown hotels and on Formica-top tables in Wheaton. They spent $5 to $75, accompanied by Muzak or a softly tinkling Steinway. Some stood in line, piling their plates from buffet bruncheonettes. Others just stood in line, waiting for a table.

In Washington, Sunday brunch has become an institution second only to church-going. It is also becoming the most popular -- and affordable -- way for families to enjoy a restaurant meal.

"It's an interesting phenomenon, said John Laythan, co-owner of Clyde's the Georgetown eatery that claims to have spawned the area's brunch crunch in 1966. "At that time, almost no place was open on Sunday."

Yesterday, his restaurant expected to serve more than 1,000 brunches, dishing out the highest volume of food for any one meal during the entire week. It was the same scene all over town.

"Sunday brunch is the busiest day we have all week," said Kevin Connor, the portly, mustachioed manager of The Man in the Green Hat, a Capitol Hill pub. "I used to have a restaurant outside of Boston. The brunch was moderately successful, if that. Down here, it's just amazing. I can't understand it."

Connor glanced at the crowd jammed into the neighborhood restaurant and shook his head in disbelief.

"I never heard of going out for brunch in Wilmington," said Kerry McKenney, a blue-eyed Delaware native and aide to Rep. Dawson Mathis (D-Ga.). "But when I first came to Washington somebody said we'll have to get together for brunch. I realized it was kind of an important social scene in Washington."

At a nearby window table, Department of Transportation anaylst Joe Young and his wife, Jane, entertained weekend guests visiting from New Jersey.

"It's just the cosmopolitan thing to do," Young said of Sunday brunch noting that Washington is a city populated by many apartment dwellers. "People don't have to go out to the back yard and see the lawn," he said. "They pay rent and go to brunch on Sunday."

A few doors down Wisconsin Avenue, The American Cafe ran out of waffle batter midway through brunch. Across town at the Sheraton-Carlton Hotel, a white-toqued chef stood beside elegant ice carvings, replenishing the more than 60 brunch delicacies served in the city's most sumptuous Sunday buffet.

The hotel began serving champagne brunch in 1927, but discontinued it many years later. General manager Rose Narva revived it in 1976. Mayor Marion Barry brunches there. So do White House Social Secretary Gretchen Poston and Chief of Protocol Evan Dobelle, not to mention diplomats, politicans and blue-jeaned families. The fixed-price brunch runs a little over $18 per person.

According to restuarateurs, brunch is a money-making meal. Food items are relatively inexpensive, turnover is high, the all-you-can-drink champagne is from California and gussied-up egg dishes are easy to mass produce.

Which is fine with the brunch crowd.

"I'd rather try a new restaurant by having brunch there than by having dinner there," said Laurie Bayless, 25, who was brunching at Chadwick's in Alexandria yesterday. "It's a lot cheaper."

Over in Georgetown, Michael Baum and his wife Harriet and the attraction of brunching at Jour et Nuit is largely economic.

"I'm sure it would cost us three, four, even five times more to go out on a Saturday night," he said. "This way we can have our times out at a restaurant and get a good meal at a fraction of the cost with no hassles."

Eight-month-old Naomi Baum, dozing in her stroller yesterday at the airy, green-terraced restaurant, has a wealth of experience with brunching. She attended her first brunch with her parents when she was 2 days old, and has made it a weekly practice ever since.

"Brunch had become such a ritual for us that we had it in the hospital the Sunday after she was born," said Chevy Chase ophthalmologist Baum, who with his wife as been coming to the restaurant's Sunday brunch for the past two years.

"When I saw (Harriet) was going to be in the hospital on Sunday, I came down here and arranged to carry out brunch," said the work-shirted Baum through bites of Eggs Benedict -- standard brunch fare in most parts of the nation's capital. "It was terrific."

Naomi, her parents said, is "not into" brunch -- yet.

Across the street at Clyde's, Irene Kountouris -- in a low-cut, slinky black dress -- was sipping a drink in the crush of the crowd. "I think a lot of these people are tourists, or people having the morning after the night before."

Indeed, one restaurant critic noted, the enormous popularity of Sunday brunch seemed to originate with the singles crowd and the so-called "New Morality."

"I hear women friends of mine making a date for Saturday night and saying, 'Shall we plan on brunch?' It's a way of ending the night before."

Another food critic said, "When people stood going to church in the mid-60s, they started going to brunch."

The inspiration may have come from New York, or even New Orleans where breakfast at Brennan's has long been a elegant weekend repast.

Coined by the English in the 1900s, brunch -- as noted in the 1935 Webster's Second International Dictionary -- is a colloquial term for "a late first meal of the day that takes the place of both breakfast and lunch."

It became popular as elegant post-wedding feasts and after-the-hunt meals.

Although Clydes' maintain it was the first restaurant in Washington to offer the meal, which had previously been confined to private parties, the Madison Hotel has been serving "Sunday English Brunch" for the last 15 years. Normally, eight tuxedoed waiters serve between 80 and 100 brunches in the Montpelier Room from 11 a.m. to 3 p.m. The average cost is $20 per person, with corned beef hash (topped with a poached egg) going for $10.50.

"Most of the people are wealthy," said one waiter. "They have to be to eat here."

A typical customer at The Mill Mining Co., however, a popular brunch spot in Annandale is "a person out for a good deal," according to manager Jeffy Vreeland. Vreeland said his patrons take advantage of the freebies offered by the eatery, which include a salad bar loaded with fruit, bagels and sweet rolls to accompany the egg dishes.

Meanwhile, not all brunchers are Eggs Benedict bound. In Wheaton, the Chinese restaurant Tung Bor offers more than 40 different varieties of dim sum pastries, savory steamed dumplings served in tea houses in China. The restaurant does not take reservations, and a line ususally forms outside the pagoda-like building 30 minutes before its 11 a.m. opening.

"For some people it's breakfast, for others it's lunch," said customer Hubert Lee, who ate Sunday brunch with two friends for $15.

Another customer, Sidney W. Popkin, said he and his wife had driven more than two hours from Bristol, Pa., to brunch at the Tung Bor. Popkin, who said he had traveled twice to China, rated the restaurant's dim sum as the "best in the world."

Back at the Old Town Holiday Inn in Alexandria, one elderly woman surveyed the Sunday feast of salads, bagels, cream cheese, scrambled eggs, barbecued meats, vegetables and desserts. Brunch, she said, was a longtime tradition in her family. "You'd go to church, get brunch, go home, get into old clothes and enjoy yourself," she said.

Howard Carperner, a St. Louis resident visiting Clyde's yesterday morning, had a different philosophy. Sipping a prebrunch Harvey Wallbanger, the frizzy-haired attorney said, "There's nothing like getting blasted before one in the afternoon."