This year's Washington Cherry Blossom Festival will feature Roy Rogers and Dale Evans, hang gliders and 376 trombones led by "The Music Man" composer, Meredith Wilson.

But it probably will be missing what also was missing from last year's festival and numerous others in the last decade: cherry blossoms.

Last year, unusally cold weather delayed the blossoms until after the end of the six-day festival and parade, Washington's largest annual tourist attraction. This year, spurred by unusually warm, wet weather during the past 11 days, the blossoms are expected to burst within the next three weeks -- a week to 10 days before this year's festival begins March 30, according to James Lindsay, chief horticulturalist for the National Park Service here.

The blossoms could easily appear before March 20, the earliest they have ever bloomed since the Japanese cherry trees were planted in 1912, Lindsay predicted yesterday after touching and examining the cherry buds at the Tidal Basin.

"The bud casings already have split, so all we need is a couple of weeks of mild weather, then four or five days of warm sunshine and bam, they'll be out," Lindsay said.

Mild weather is exactly what the National Weather Service is forecasting through the middle of March, though perhaps not the average 20-degrees above normal temperatures the Washington area has enjoyed since Feb. 14.

The warm rain, almost two inches of rain in four days, alone, not only started the sap flowing in the cherry trees and other local flora, but apparently in one week relieved the threatened summer water crisis for Northern Virginia. The Occoquan Reservoir, which supplies most suburban Virginia residents, received about 4 billion gallons of water in the last week of rain, putting the 27-year-old reservoir's water level higher than it has ever been, partly because the height of the dam was raised two feet last summer.

Washington's cherry blossoms have been the harbingers of spring and the tourist season here ever since March 27, 1912, when First Lady Helen Taft and Japanese Vice Countess Chinda planted the first of the 3,500 Yoshino cherry trees that now ring the Tidal Basin. The two trees planted then still stand beside a Japanese stone lantern and the Kutz Bridge, near where 17th Street NW ends a short distance from the Tidal Basin.

The Yoshino cherries are the earliest flowering trees to blossom, horticulturalist Lindsay said, "but the florets are delicate" and the pink blossoms can be killed by frosts or blow off by traditionally gusty March winds. In 1976, freezing temperatures nipped most of the cherry blossoms in the bud, Lindsay said, and strong winds the following year deflowered the trees the second day the blossoms were out.

While cherry blossoms are fragile, most spring flowers are hardy and even if they bloom early, will not be destroyed by frosts, Erik Neuman of the National Arboretum said yesterday. Forsythia, crocuses and some tulips and other spring flowers already are in bloom in sheltered spots around Washington.

The 1970s were a bad year for both the cherry blossoms and the Cherry Blossom Festival, when the blossoms and the festival coincided only half of the time.

"We can't predict the weather a year in advance," festival parade coordinator Nick Evers said forlornly on hearing this year's Park Service blossom forecast. "All we can do is plan the festival as close to April 5th as possible -- that's the average date they've bloomed over the past 50 years." a

Linday said the figures actually show April 8th to be the average blooming date, although the trees have bloomed as late as April 18th in a cold spring in 1958 and as early as March 20 during warm springs in 1927 and 1945.

Even if it's a blossomless festival, "we've planned lots of new things this year," Evers said. The parade April 4th will be on national television for the first time, and will include a special 49-band tribute to President Reagan on the Ellipse, "with The Music Man, Meredith Wilson, leading not just 76 but 376 trombones," Evers said.

Roy Rogers and Dale Evans were offered palomino horses to ride in the parage, but the two film and hamburger chain stars, now in their late 60s, have opted to ride in a limousine instead.