It's a homecoming celebration, that's what it is, complete with floats, parade and princesses.

In this small town known as The Nation's Capital, the cherry blossoms are the only thing assured to pull the neighbors out. Cars crawl around the Tidal Basin for a wee, tourists clamor for rooms, but this is the local ritual of spring and Washingtonians can't stay away.

The cop on West Basin Drive gives up trying to direct traffic and instead spends his day calling out to passing drivers whose inspection stickers have expired. Near the Japanese lanter, fathers and sons and women in bandannas hang over the bridge to fish and dangle their lines in the Tidal Basin, as usual. But this week, the lantern's lit.

Pink petals fill the air and waft on their own sweetness. Washington gets proud. Is isa, after all, a beautiful city, but especially in Arpil.

Around the Tidal Basin, Washington Monument and Hains Point, there are 3,500 cherry trees, and everbody's monumental question is, When will they bloom? National Park Service experts were out Tuesday a week ago, and spokesman George Berklacy says, "The buds wer e beginning to swell, and tinges of pink were beginning to show." They predict that barring cold snaps, the blossoms will come out on April 4th.

Whatever, the Cherry Blossom Festival goes on year after year, hit or miss the blooming trees, SUNDAY at 8:30 in the morning, the celebrating takes off with the seventh annual Perrier Cherry Blossom - a ten-mile race that loops around West Potomac Park on Ohio Drive, Hains Point, East Potomac Park and the Tidal Basin.It's too lateto sign up - 4,035 run- ners beat you to it, including marathoner Bill Rodgers, who won the Perrier last year and holds the course record of 48 minutes, 57 seconds. About 800 of the runners are women - an increase of 25 percent over last year. Kids are racing, and even a few people in their 60s and 70s.

Meanwhile, spectators can hold up banners, hand off orange sections and water to the runners, and cheer. This is the first major race for some of these folks, and they need the encouragement. Best vantage points for spectating are the start/finish line at the northern tip of Ohio Drive, near the Lincoln Memorial; at Hains Point, where Rodgers broke from his pursuers last year; and by the Jefferson Memorial, which the leaders should be passing on the last leg around 9.

For those runners who can't just watch, but can't handle 10 miles either, a two-mile "fun run" starts shortly after the big race. Sign up at the start/finish line by 8:15. The idea is just to finish, but some runners are more competitive; If you are and find yourself running last at the halfway mark, stride into a bunch of spectators and no one will ever know. The first 2,000 finishers win a patch.

Another sign of spring that happens Sunday: The Smithsonian changes to summer hours, 10 to 9, through Labor day.

Monday evening at 7:30 by the Tidal Basin, the 67th Cherry Blossom Festival officially begins with the lighting of the Japanese Stone Lantern. The lantern dates back to 1651. The design called for torch illumination, but the modern age has rigged it with an electric light, and, and that, just for the evening. This year Hisako Matsumuro, eighth-grade daughter of a minister at the Japanese embassy, will do the lighting.

Wednesday, in the Shoreham Americana, the 53 Cherry Blossom princesses will be introduced at a luncheon and fashion show. They come from all the states expect Delaware, and from the District of Columbia, American Samoa, Puerto Ricco and Guan.

Next Saturday, April 7, is a big day for the blossoms. The seventh annual El Toro regatta starts at 9:15 on the Tidal Basin. There'll be about 40 of these eight-foot sailing dinghies to watch and take pictures of, with the trees as backdrop.

Then at 11, the Cherry Blossom Parade kicks off, between 7th and 21st Streets NW, on Constitution Avenue. There will be 27 bands and 19 floats - four of them the big balloon kind. Grandstand seats are hard to come by, but there's curbside space between 17th and 21st streets. If a crowd blocks your view, you'll know the parade's going by when you see a Carter peanut and a Pillsbury doughboy 75 feet overhead.

Saturday night is, for at least 53 people, the culmination of the festival. It's the Cherry Blossom Ball at the Shoreham Americana, where the Japanese ambassador, the mayor and, again, little Hisako Matsumuro, spin the wheel that decides who will be Cherry Blossom queen.

Spring's beauty in Washington begins with Cherry Blossoms, but it doesn't stop after the first week in April. Berklacy predicts the town tulips will bloom "on the heels of the cherry blossoms." Near the Tidal Basin and Independence Avenue, the Park service has hand-planted an almost embarrassing number of bulbs - 490,000. Just off Independence there's a tulip library, where thousands of bulbs are filed to flower in unison.