Washington is loaded with comedians and sources of great humor. But after the politicians, lobbyists and lawyers have gone home for the weekend, things aren't so funny. Every Thursday to Saturday night, though, there's still the Comedy Cafe to tickle your funnybone.

A garden of largely home-grown comic talent, the Comedy Cafe is home to many of the area's funny men and women who call comedy their profession or, at least, their avocation. The cafe is also the site where hopeful comedians crash and burn.

Glossy poster-size photographs of chimpanzees hang from the brick walls, showing chimps dressed as Arab sheiks holding a gas pump, stomping on a Mercedes-Benz or brushing their teeth over a toilet. Tacky, but amusing. Potted philodendrons hang from the ceiling while carnations stuffed in mineral-water bottles top the checkered tableclothes. A pay phone clings to a pillar in the center of it all. Clearly a room in search of an identity -- just like the performers.

Jay Keating, for example, was always "a smart mouth" when he was growing up in Falls Church. Now at 29, he's trying to use that misunderstood attribute as a professional comedian and can often be found at the Comedy Cafe several weekends a month and working for free on many Thursday nights during open-mike.

Using his folk guitar, Keating sings '80s- style lyrics to '60s pop-rock tunes. One song takes a futuristic look at an aging Rolling Stone, Mick Jagger, singing the blockbuster hit "Under My Thumbs":

"Under my gums, I see a wrinkled bag who once had a face . . . Under my gums . . ."

The Preppy version of Bruce Springsteen's "Born to Run" is renamed "Born to Be Chauffeured" and a spin-off of "Love Story" becomes "Biff, Prep means never having to say I'm thinking . . . ."

Open-mike nights offer the good, the bad and the awful -- all in one evening -- and have one great advantage: They're cheap. A cover of $2.49 buys an opportunity to see young local comedians and, on occasion, proven performers from Philadelphia and New York. Gregory H. Poole, Andy Evans, Dan Brenner and Roger Mursick, leaders in the local talent pool, often use open-mike shows to tune up their acts and test new material. Often the results are hilarious. But the flip side is that a lot of acts just aren't funny, embarrassing the performer and the fidgeting audience.

Recently, for example, a young comedian conducted a ventriloquism interview using a Ronald Reagan dummy and taped responses. The evening's hard-earned momentum came to an abrupt halt when the tape malfunctioned. Another time, the MC's Groucho-like remarks about a patron's out- of-style suit were volleyed back via a waitress who was taking a drink order: "Yeah, bring me a comedian and make him funny!" "Make me laugh!" is a favorite line of hecklers.

The more polished performers -- people like Sam Greenfield -- don't have to worry much about "bombing." Greenfield, 35, a comedian for the past year and a half, is now a Comedy Cafe regular with a fast-paced, 30-minute routine covers a gamut of subjects.

"The president is a real smart guy. . . didn't even know he was shot," says Greenfield in his running commentary on current events as he stops to ask, "Should the PTL Club be renamed 'Pass the Loot'?"

Adding a local touch, Greenfield recalls the fictitious insurance company, "Mutual of Gaithersburg," whose advertisements featured a woman complaining, "I'm covered like a matchbox covers an elephant's behind!"

"Laughter is contagious," says Comedy Cafe owner Dan Harris. But when the laughter isn't spreading, Harris flicks on the red light to end the act. Would he try a routine himself? "I'd be too embarrassed."

The Comedy Cafe kicks off a six-week amateur "Joke-off" on June 16, open to anyone willing to go for the gusto. It's co- sponsored by comedy radio station WJOK (1150 AM), which will air the winners. The two categories -- best joke and best stand- up comedian -- will be judged each week by professional comedians and celebrities. Prizes include a private lesson by comedy instructor and FCC lawyer Dan Brenner and a chance to be paid for a night's performance. WHERE THE JOKES ARE -- The Comedy Cafe is at 1520 K Street NW. Cover is $5 for shows beginning at 8:30 and 10:30, Friday and Saturday, and $2.49 on Thursday, beginning at 8. Reservations suggested. Call 638-JOKE.