An estimated 65,000 good-natured stoics gathered yesterday on Constitution Avenue for Washington's traditional Cherry Blossom Festival parade, despite heavy rains and 15-mile-an-hour gusts of wind that added an extra edge of chill to a 53-degree day.

The weather was a disappointment both to residents who have not seen a sunny weekend since March 12 and to tourists who came to Washington with parades and clear skies in mind. Area residents could look forward to more bad weather in the next two days, according to National Weather Service forecasters, who issued flash-flood warnings for much of western and southwest Virginia and predicted rain today and Monday.

Yesterday's rain did little damage to the two-hour parade's 15 floats, which were made largely of plastic. But it did put a damper on the main attraction: more than thirty marching bands, about half of which struggled through the 10-block walk with soggy uniforms and flags and rain-dulled instruments.

"I knew, I just knew, it was going to be a beautiful day--and look at it!" sighed Judith Miller, whose firm had prepared a large float with an Oriental motif for the occasion.

For the second time in two years, paraders defied the elements in order to strut their stuff.

"The excitement keeps you warm," said a radiant, chiffon-clad Gail Brent, one of the cherry blossom princesses. Other paraders tried to stop shivering by jogging in place during the long wait before their turn to march.

The members of the city's Cardozo High School Marching Band practiced their complicated dance routines repeatedly under the watchful eye of bandleader Richard Gill.

"The boys' uniforms are made of wool," he said, "but the girls will just have to hope for the best." Four majorettes in tiny white skirts and bare legs looked cold and glum.

When 12:30 struck, the crowd, estimated at 65,000 by police, watched indifferently, one eye on the clouds, as Effi Barry, the mayor's wife, and other dignitaries drove by in open cars. The real parade, people knew, started when the Cardozo band, the first in the parade, drummed the gathering to attention with three sharp beats.

By the time gray clouds, which had threatened the parade earlier, drenched the crowd gathered along Constitution Avenue, many spectators were already shaking. "It's freezing cold, but we intend to stay," said Edgardo Abarzua of Chile, who was watching the parade with his shivering wife.

It was a bad day for paraders, parade-watchers and most of the vendors in search of festival customers. The hot dog seller was disgruntled. "No business, nothing!" complained Anastasia Arvanitis, huddling under the eave of her stand as the rain began to pour. But the savvy few who switched from their usual wares to umbrellas made a killing. By 2:30 p.m., one hour after the downpour began, one vendor, Paul Stokes, had sold the last of the 50 umbrellas he brought for the day.

The rest of the marching bands, shriners, and cherry blossom princesses were rewarded with thinning but still substantial crowds. One definition of style is grace under pressure, and the teen-agers from Anacostia High School showed plenty of it in their high-stepping, strutting display at the height of the downpour.

Watching them, a drenched but bright-eyed Renee Levesque, stationed here with the Army, summed up her feelings: "If you don't rate this parade a '10' just for sticking it out you have no business being here."