SUMMER THEATER, like the season itself, is an evanescent thing -- its brief and furious burst of energy fades with the season, eclipsed by the more costly splendor of the intown stages.

But though the Washington world as we know it all but stops for summer, the lights don't go down when the heat is on.

Some of the old maxims still have a little life left, and "the show must go on" is one of them. The summer months are packed with cool pleasures, among them summer theater and festivals in the city and in out-of-the-way places you may encounter in your travels.

Even the theater has a summer place. But what's in it for the audience? What makes summer theater different from the stuff that treads the boards the rest of the year? What could possibly urge summer audiences to leave their air-conditioned cocoons?

Maybe it's the easy informality, alien to the in-town theater. At most of the summer stages, you're as welcome in T-shirts and shorts as in sundresses and seersucker suits. Or maybe it's just something to do to escape the heat-induced doldrums.

Whatever, there's plenty within driving distance -- the polished professionalism at nearby, neighborly Olney Theater, the Washington area's only professional summer theater; the historical pageantry at Virginia's Rock Kiln Ruin Theater; the annual community musical at Arlington's Lubber Run Amphitheater; and much more -- indoors, outdoors, in and out of town.

"There is no such thing as a summer vacation if you work in the theater," says Linda Reinisch, one of the directors of Washington's Woolly Mammoth Theater. Other theater professionals echo this response. Acting isn't just an adventure, it's a job.

"We need theater -- we need it year round, not just nine months out of the year," agrees Olney Theater director Bill Graham, Jr. "We need to find entertainment options out of more than our VCRs. Summer theater fills the gap left when the regular theaters go dark for the summer. And it gives actors, and newcomers, an opportunity to do more work, and for audiences to know theater is always there."

And actors and directors who have known the pleasures and perils of performing for people with the glow of sunburn and sand still in their hair know that there is a way to combine work and play.

Richard Thomas, who just finished playing the title role in Peter Sellars' massive "Count of Monte Cristo," did his first summer tour at the age of 10, taking a show called "The Critic's Play" up and down the eastern seaboard. No sooner was his Kennedy Center dressing table cleared than he was off to the Williamstown (Massachussetts) Summer Festival to play the lead in Howard Fast's new play, "Tom Paine."

"I work with Williamstown in the summers because it's a complete theatrical environment as well as a family environment," Thomas says. "There's baseball and swimming for the kids 9Thomas has four0, they can run around barefoot -- and dad gets to work."

These days the word for summer theater is "summer stock." And though some of its settings have remained nostalgic, they've all had to face the music.

Summer stock is perilously close to extinction, according to a recent Actor's Equity's study. The number of Council of Stock Theaters (COST) stages has dwindled to 17, from 33 in 1979. The state of summer theater reflects Broadway trends, and the dearth of new product there has been widely bemoaned. And new producers are not entering the summer arena.

And somewhere along the line, fairly or unfairly, summer stock seems to have picked up a reputation as a last-ditch haven for "The Love Boat" People -- jaded (or faded) television and film performers.

Also, tastes in popular entertainment have shifted -- where once the whole family might pile into the car and drive out to the summer thater in the woods for after-dark fun, today's vacationers, after touring or sunning, can opt for a rock concert, or more likely, watching TV or MTV or slamming a first- run movie into the VCR.

No more can a converted barn and an enthusiastic bunch of fresh-faced kids make a go of putting on a show. Like everything else, production and union costs are up. And extravaganza-bred audiences won't settle for shoestring shows. A misstep in choosing a play can be a financial disaster. Producers can lure crowds in by plugging in a TV or movie "name," but many of them are prohibitively expensive.

Gone forever are the days of what was known as the "straw hat circuit" or "citronella circuit," where performers would present frisky summer fare under tents and pavilions and remodeled barns or town halls.

Time was, the big-name stars would travel on their own from burg to hamlet, joining up with local troupes familiar with their warhorse vehicles. It was an era immortalized in movies like Judy Garland's"Summer Stock" and "Marjorie Morningstar."

In more recent memory, you could depend on seeing such perennial pass-throughs as Ann Corio's "This Was Burlesque" or John Raitt in the umpteenth tour of "Oklahoma."

But it's goodbye to all that.

"The straw hat stuff just couldn't pay its own way," says Olney Theater artistic director James Waring. "That one- week-run kind of thing, the audiences were just coming out to see the star in classy clothes." (And what, after all is "Dynasty" all about?)

But enough bellyaching. Summer theater is by no means a thing of the past.

Somewhere between the rustic straw hat days and the sophisticated urban theater is the Olney Theater, a vigorous survivor. The first professional summer theater south of the Mason-Dixon Line, it has stayed healthy by evolving. Now, during its 16 operational weeks it offers not only musicals and comedy, but also "difficult" plays by the likes of Pinter and Stoppard. And it really stirred things up in the '60s with an absurdist theater festival.

Celebrating its 33rd season, and sporting since 1978 the title of "the state summer theater of Maryland," Olney is one of the last of those neat old wooden theaters -- it looks like a set out of Judy Garland's "Summer Stock," and it smells like summer inside: cool and piney. The house lights are housed in inverted bushel baskets. That's country.

After a relaxing exurban drive past luxuriantly green cornfields, daylilies and roadside vegetable stands (and condominium developments and fast-food outlets), Olney audiences linger as they've always done on the flower-decked fieldstone terrace before the show. Or they wander the 16-acre grounds, where at a matinee intermission you can watch apprentices painting flats. There are few things more cozy than being inside the Olney's barnlike roof watching a show, while the rain drums faintly on the roof and the low grumble of thunder punctuates the drama.

Used to be a giant hickory tree grew right smack in the middle of the lobby at the Olney. And they rang a farm bell to call the meandering audience back to their seats from the lemonade stand out back. Hopping into the Wayback Machine, one could see a time when stars such as Helen Hayes (in "Alice-Sit-By- The-Fire") and Tallulah Bankhead (in "Private Lives") and Lillian Gish, Laurette Taylor, Luise Rainer, Kitty Carlisle and yes, ZaSu Pitts used to stalk the stage there. And when future Washington stars, like Arena's Halo Wines, worked at Olney as teenage apprentices, scrubbing flats and painting seats.

The hickory tree is gone now. And as James Waring says, the area is now more suburban than country.

But they still ring the bell to hail the audience. And at the beginning of the season, before the corn gets high, and toward the end of the season when the corn is harvested, you may see whitetail deer foraging in the fields.

Things have gotten a bit more sophisticated -- the 720-seat theater and offices are air-conditioned and computerized now, and the stage (which can house two set changes, a luxury intown directors might well envy) has seen works by Ionesco and Stoppard and the world premiere of Hugh Leonard's Tony- winning "Da." But that summer feeling survives.

Over the years, some of the area's best performers and technicians have been found "out in the country": Arena's Stanley Anderson, the Folger's Jim Beard; actresses Marcia Gay Harden and Brigid Cleary, music director/pianist Rob Bowman. And a good number of Washington actors can thank the Olney for giving them their Equity cards.

In fact, Olney, like most summer theaters, sees itself as a breeding ground for up-and-comers. "Each summer we begin with rank amateurs and by the end of the season, they're ready to move on," Graham says.

It's a family affair -- Bill Graham Jr. was managing Toby's Dinner Theater four years ago, until he stepped into his father's shoes as Olney's managing director (Bill Sr. worked at Olney for 30 years); Chris Bauer, 14, son of actors Richard Bauer and Halo Wines, is working as a "slab boy," building sets.

Olney was purchased in 1942 by philanthropist businessman C.Y. Stephens, owner of the High's Dairy chain, and it presented "star packages" until it was taken over by the University Players in 1953. Since then, Olney has been one of the few summer theaters that produces its own plays, instead of booking a summer package from New York.

"We're proof that summer stock doesn't have to be light comedy or fluff," Graham says. "Competition in Washington is very different now -- in the '60s there was no Kennedy Center, no Arena, no dinner theaters, and community theater was very small, and people would turn to us. So we've done a lot of things you wouldn't expect from a summer theater.

"It doesn't take names to do good theater, and we prefer to do good theater. We're not overly concerned if it's a big-name play, or if it's been done somewhere else, or whether it's going to make us a lot of money.The idea is always to do what we can do best, and we tend to stick more with the Washington theater crowd -- the Richard Bauers, the John Neville-Andrews."

Aside from the minor matter of fiscal necessity, working in summer theater can be a rare pleasure for actors, after a day of the intense pressures caused by a two-week rehearsal and production schedule (most in-town theaters have four to five weeks to rehearse).

"It's an enjoyable place to work," says Waring. "The actors roll out of bed at 9, eat a bit of breakfast, take 15 steps and they're onstage."

Out at Olney, performers live on the premises in the Actors Residence, a rambling, restored 1880s farmhouse, with an atmosphere (and a swimming pool) that lures city-weary actors. "The actors are very happy here," Graham says. "In fact, most of the actors who come out here more than once refer to it as 'Camp Olney.'

The big airy rooms of he house, which does resemble a summer camp mess hall, are strewn with actorish clutter; and these days, you're far more likely to catch cast and crew sprawled in front of a rented video movie than playing a game of checkers.

But the camaraderie and spirit of retreat remain. After a full day, Graham says, the long front porch is usually busy with talk and gossip and poetry until 2 a.m.

Memories: Actor Richard Bauer cooked and served a 3 a.m. "strike" breakfast of scrambled eggs and bacon, after the crew of "Enter a Free Man" disassembled the set at the end of the run. And Tom Toner, one half of the cast of last year's "The Gin Game," made a habit of cooking a Sunday dinner for everyone between matinee and evening show.

Sometimes country and nature conspire to produce some sight gags that couldn't be written into any script. Nature-lover Bauer recalls doing "The Rose Tattoo," which calls for a black goat. "They scoured Maryland and Virginia and finally located one in West Virginia. Just a darling kid with a charming face and these little tiny nubbins and a little tuft of white hair. It absolutely hated performing -- it was very funny listening to Jim Waring talk about having to get the goat onstage." Waring remembers having to coax the goat with baby bottles full of milk, and an occasional swat on the rump, which the goat reciprocated as soon as your back was turned. Bauer's pal wound up giving him poison ivy, and as he had to perform in English woolens in a typical July, it was a particularly uncomfortable season.

And another time, Bauer says, a "gorgeous" mother raccoon and her babies established residence above the backstage area. "One night an actor was just about to go on, and he said, 'Uh- oh, it's raining.' Of course, no one had heard any thunder or seen any lightning -- it was just the mother raccoon giving him his 'cue.'

It's "that sense of summer," Bauer says, that makes working at Olney and elsewhere a treat instead of a necessity for actors. "It's not camp exactly, but that combination of work and vacation, where you work your tail off, but at the end of the day, you know you can really relax."

And Graham says he enjoys greeting the Olney's loyal "regulars," some of whom have been sitting in the same seats for more than two decades, and he likes talking to the ladies of summer in their floral hats and cotton frocks who have made the jaunt out to the country on a Sunday afternoon.

"We are truly the last of a dying breed," Graham says, speaking for the Olney, and perhaps for the rest of the dwindling summer stock circuit. "Because once this is gone, it's gone. Fifty years from now, people who have had this experience -- going to the summer theater or working here -- will have to tell their children or grandchildren about it."

"Summer theater is what every aspiring young actor thought theater was going to be like, then found it was a business and left," Graham says. "We still have it here in the summer."