For months, mild-mannered Keith Parker would hop on the Metro after a long day at a telecommunications job. He would duck into a small building on 14th Street, where he would become -- Source Theater's literary manager.

There, in a tiny office dubbed the "Lit Pit," Parker filled his nights with the feverish fantasies contained in the five teetering stacks of multicolored scripts that still surround his desk.

All this loving labor was for Source's seventh annual "A Washington Theater Festival," a considerable explosion of theater activity which begins July 13 and runs through August 11 at Source's two 14th Street stages.

Parker and his team of 38 volunteer play-readers plowed determinedly through the 452 new plays submitted for festival consideration, including a record 115 from local playwrights. The field was narrowed down to the 70 or so that will provide about 200 acting roles for this year's volunteer festival performers.

"Back in time when {Source Theater founder} Bart Whiteman and {Studio Theater founder} Joy Zinoman and {New Playwrights' Theater founder} Harry Bagdasian were starting the small theater wave," Parker says, "Bart felt that Washington should have a festival like other towns do, and he set it up on the order of international festivals, with an emphasis on new plays. If it works, you should be able to see all these playwriting and performing groups and come away saying 'Look at all this theater going on in Washington.' "

This year, the festival emphasizes thematic groupings -- a pair of mysteries one night, a trio of Vietnam plays the next, four short comedies the night after that, and so on.

It's also one of the best entertainment bargains in town: The costliest seats are $8, for "Festival Focus" plays, which receive four full productions. Seats range from $3 to $5 for "Festival Fringe" productions -- which may be full productions or script-in-hand performances, the "air-conditioned matinee series" and "Festival Late Night" shows, which feature off-the-wall stuff at midnight for the "Saturday Night Live" set. Call 462-1073 or stop by Source for a schedule.

Some playwrights, Parker says, put more effort into attracting attention -- one left his psychiatrist's prescriptions bound into the back of his script. But the most crucial element was a clear synopsis -- and a good play, of course. "You really have about three minutes to get someone's interest in reading a play," Parker says.

Parker instructed his play-readers to beware typical playwright pitfalls, including: "the Well-Crafted Bore, in which nothing is wrong -- but nothing is right. The Hybrid Hit, in which the Sam Shepard cowboy meets a Beth Henley cheerleader in an Edward Albee living room. And then there's This Year's Crop, which were divided between the Geraldo Rivera news headline plays or the 'Les Miserables' history-as-you've-never-seen-it-before epic plays."

Parker says he rewarded his burnt-out readers with a look at his cache of category-defying entries, "like the country-western musical version of Milton's 'Paradise Lost,' or the one in which three Las Vegas showgirls are the only survivors of a nuclear holocaust."

Having tackled the thankless task of making the fantasies of others come true, it seems only fair that the festival provide Parker the opportunity to exercise (or is that exorcise?) his own infrequent acting itch: "I've been offered the role of the shag-carpet monster in Deborah Pryor's 'The Man From Planet 52,' " he says. "In fact, I'm fighting for the role."

Is less really more? One of the highlights of the Source festival (at least in the opinion of critics and columnists who have been overheard to say "the shorter the better") is the annual 10-Minute Play writing competition. This year's selection of quickies from Washington writers and media figures includes "Brood 10: The Cicada Play," by Bill Freimuth, director of last year's "Titus Andronicus"; "Massive Retaliation," a pushing-the-button play by Woolly Mammoth literary manager Neil Steyskal; "The Great Australian Rabbit Trick," which playwright Amy Schmidt tells us is "a satire on cancer research"; and the one we've all been waiting for, "Bikini Girls From Mars," by a committee of writers, many of whom will remain forever anonymous.

This year Source opens the competition to the theatergoing public on a limited basis (revenge, anyone?). The first 25 entries they receive by July 15 will be considered for production in this year's festival; the rest will automatically be considered for next year. Stuff scripts in an envelope and mail them to Keith Parker, 10-Minute Plays, 1809 14th St. NW, DC 20009. It could be the start of something . . . small.

Several actors and designers from Studio's production of "As Is" participated in Sunday's 10K walkathon which raised more than $175,000 for Washington's AIDS education and service programs. Studio actors Michael Chaban, Tom Kearney, Mark Mendez, Michael Russotto, Kimberly Schraf, director's assistant Keith Baker and hairstylist Rivon Shaneyfelt were among the nearly 3,000 who walked -- but the rest of the crowd didn't have to rush back to make a 2 p.m. matinee.

Because of Fourth of July festivities, both Sunday performances of "As Is" have been canceled. On Monday, Studio will turn the theater over to the Whitman-Walker Clinic for an outreach program called AIDS 101, featuring "The AIDS Movie," a locally produced videotape about how the disease affects all groups, and an informal discussion with Dr. Michael Sanders of the George Washington University Health Plan. The free program begins at 8 p.m. Call 332-5295.

Bulletin Board: Because of the July 4th holiday, Colleen Dewhurst's "My Gene" will close after Friday's performance. Tickets for Saturday's performance may be exchanged at the Terrace Theater box ofice . . . "Nunsense," though, will present a half-price show on the Fourth. Curtain at Ford's is 6 p.m. so everyone will be out in time for fireworks . . . "Stars Out Tonight," by Washington playwright Mark Berman, was a runner-up in the Texas-based Margo Jones Playwriting Competition. The play, about five actresses from the '50s and '60s who meet at an audition for a horror movie, is being considered for production in Washington this fall.