WHENEVER Ken Harvey comes into a room where there is a piano, he has to go over and make friends with it.

Some he gets along with fine, some he doesn't. But they always have to be introduced.

Right now he's pretty good friends with the Baldwin at Mel Krupin's Lounge. He comes on at 8:30, or soon after (his friends call it Ken time). Setting coat and gloves on the bench, he fetches from the bar a hot coffee in a lowball glass and a snifter of brandy and arranges them on the piano with his cigarettes and reading glasses. He wears slacks and a dark sweater and a neat scarlet string tie that goes with his billowing blond hair.

Then he starts to play.

It's a "Porgy and Bess" medley, loaded with extras, fanciful curlicues, glittering glissandi that run cleanly all the way up the piano's spine. One song flows into another before you know it.

"I have to loosen up," he says. "I'm usually shy at first. I'm terrified every time I start." He has been doing it for 11 years, which adds up to a lot of terror. He first played violin at 12 in the New Orleans Youth Symphony, went on to the Birmingham Symphony, mastered 11 instruments, majored in music (theory and composition) at the University of Alabama. But he got away from the classics when he took to editing scores for college musicals.

Suddenly he leans into his crane mike and tries out the voice with "It Might As Well Be Spring." A deep baritone, skillfully controlled. He keeps something back, even when he goes into the final reprise.

"Let's do a few Stephen Sondheim songs," he murmurs conversationally to the dozen people scattered around the comfortable room. These are mostly holdovers from the Happy Hour and they are talkative. His own people -- the ones who come to hear him -- don't come in until after 10:30. The final number is "Send In the Clowns," that sad smile of a song, and this time he lets it go, and the talkers stop talking and turn around in their chairs and watch him, their mouths slightly open.

"I like 'em closer than this," he says. "I wish we'd put some chairs around the piano. Eye contact is very important to me. For me, music is about communication. I love requests, because it's hard to fill an evening all by myself. I work four hours a night, Tuesday through Saturday, but I'll go five or six hours if need be." His right hand lights a cigarette. The left hand keeps on playing.

The closest he gets to classics these days is some rearranged Strauss or the Moonlight Sonata with a vocal of "My Funny Valentine." It works, curiously, like chocolate sauce on turkey. Sometimes an audience will be on a Kurt Weill kick, people setting each other off with ideas for requests. Often the whole evening will have a theme, a period like the '60s, or a mood. Once he wound up playing songs from World War I and II for two hours straight.

"I have absolutely no idea how many songs I know. I have incredible retention of words and music. My family wasn't musical, but my mother did sing a lot around the house, and I must have picked them up, though I don't remember it." Of course he can't trot out every single song you ask for, but he can give you something charmingly close. He's rarely hassled, probably because he somehow turns each audience into a pleasant, laid-back little family.

At 31, Harvey has been a florist and model and music teacher in a Houston high school before coming to this second gig in Washington. The first was a brief stay at Numbers, where he picked up some groupies so loyal that they followed him to Texas and then back here. He likes having a regular clientele, has sworn off the resort circuit (Acapulco, Mexico City, Buenos Aires). But that tanned world still draws him.

Last year he flew to St. Thomas to get away from music. He read novels chain-fashion for two days, and then he found himself restlessly roaming the hotel patios, seeking something, he wasn't sure what. Wandering into a tiny bar, he found . . . a piano. He sat down at it instinctively. His fingers went to work all by themselves. After awhile somebody drifted in and leaned on the mahogany, and then somebody else, and then somebody else. "Can you play 'Stardust? . . .' "