SPRING ISN'T JUST a time for fevers - it's for festivals, too. In fact, some weekends there's a veritable epidemic of fairs breaking out all over the area. The spirit is infectious, so you might as well catch it in the most enjoyable way.

Since festivals tend to cluster around weekends in May and June, it's best to approach your fair-going with some definite goals in mind.

Start close to home with a visit to support your local school or church fair. Then plan to see some ethnic festivals with authentic music and dancing. On a truly glorious weekend, a trip to a distant community to cavort at their spring celebrations could be combined with a two-day getaway. And don't forget to mark your calendar for the definitely exotic, truly unusual one-day event.

Close-to-home fairs have the comfortable coziness of community effort. They're sometimes predictable, but still fun. You can expect to find rides for the kids, home-made games with immediately disposable prizes, and booths with crafts, plants and food for sale. Neighbors stroll up and down the site in a small-town atmosphere, remarking on how last year's new baby has grown into this year's toddler.

The Capitol Hill Day School crafts fair (May 13), for example, is a homey event with an artistic twist. At the Eastern Market's Gallery Five (7th Street and North Carolina Avenue NE), 22 local artisans will be displayiig and selling their "very aaffordable" works. Since that's the day before Mother's Day, it might be just he place to find that last-miniute gift - if you're flush, see Carol Reece's gold jewelry, is sampling at the outdoor cafe has drained the pocketbook, try Fred Greenberg's Notecards of Washington, D.C.

In recent years, a new inducement has been added to many school fairs: the auction. At the Horace Mann (D.C.) School Fair Saturday, the presidential connections of a well-known parent, Jody Powell, are up for bids on a tour. Powell will conduct of the West Wing of the White House. Other school fairs, such as the National Cathedral School's (May 13), also have tent auctions with bargains in such vacation homes and more common services like pet-walking an d plant-sitting.

"Theme" fairs are another popular device to bring in the neighborhood crowds. The granddaddy of these fairs, the Landon School Azalea Garden Festival, is Saturday and Sunday. For 25 years, Landon has been plant purveyor to the public, and the spectacular showing of azaleas (if they cooperate) now extends over 2 1/2 acres of luscious color. Not to be outdone in the flower field, the Cathedaral Flower Mart (May 5) also offers herbs and plants for sale beneath the carved spires of the National Cathedral. This year's theme is French Impressionism, and booth-tenders will be dressed in Parisian costumes of the 1870s.

What kind of food do you eat at the D.C. Mental Health Fair (May 7)?Brain food, naturally. The theme is "It's a Family Affair," and you can stroll through the F Street Mall downtown while learning about how to deal with "important issues affecting all of us" - being a parent, problems of he aged and minorities, working through the maze of the health service bureaucracy . . . If this proves overwhelming, you can always step into the National Portrait Gallery and seek peace through art.

Further afield, ethnic festivals with native foods, dances and crafts should also be part of your plans for spring festival-hopping. This year you can learn clog-dancing at the Irish Folk Festival and Jubilee May 21 at Glen Echo Park or study a smorgasbord of sports at International Sports and Games Day in Arlington May 14 - have you ever played "yoot," a Korean stick game; or bowled in French (petanque) or Italian (bocci) ; or tried "hurling," an Irish cross of field hockey and mayhem? How about spending an evening at St. Sophia Greek Orthodox Cathedral and sampling souvlaki, spanakopita and diples (May 19 to 21)? Or try out Brazilian, Indonesian and Mexican music and dance at the second annual Washington Folk Festival at Glen Echo Park (June 3 and 4). Debbie Hutton, who says 12,000 people came last year, promises three simultaneous stages with continous performances of international music and folkdance.

Another way to catch festival-fever is to visit communities beyond the Beltway where history and local crafts are honored and preserved.

Exchange your car for a horse-drawn wagon and tour Smallwood State Park in Rison, Md., during the "Revolutionary War Days" (May 6 and 7). There will be an 18th century encampment on the park grounds as well as performed excerpts from the musical "1776" and other events. Or shiver with a shorn sheep at the Carroll County Agricultural Center Sheep and Wool Crafts Festival in Westminister, the same weekend. Teams of one shearer and four spinner-weavers will compete in the sheep-to-shawl race. A real hair-raiser.

Over the Memorial Day weekend (May 27 to 30), Prince Fredrick will hold its ninth annual "Cavalier Days in Calvert County" festival. It's a colonial event, with four days of historic cragts and music and such foods as possum, crab cakes and country stew, English and colonial dancing, demonstrations of tobacco culture, and games and contests for the kids. This is a small but very well-organized effort, complete with guide-book for visiting Calvert County. Since the land is relatively flat, you might try viewing this festival and th surrounding area on bike - if it doesn't rain, as it has a tendency to do.

There are also some one-day festivals that offer free fun, physical involvement and a chance to learn or see something extraordinary. Like "barefoot catching and other feets" at the fifth annual "Now You See it - Now You Don't - Now You See It Again" Smithsonian Resident Associates Boomerang Cooroboree (June 10). Ben Ruhe, the resident expert on boomerangs is organizing boomerang demonstrations as well as team and individual competitions.

Most of these festivals have free admission, but you can expect to dig into your pockets for rides and food as well as for pulse purchases. There are far more festivals than those listed here, and real festival buffs should call the National Council for the Traditional Arts (296-0068) for its comprehensive nationwide list. Here are a few of the unusual area ones through mid-June.