It's 10:30 and the show is over. A drink seems like a good idea, but where? Wanting a bit more atmosphere than the cacophonic murmur of surroundsing tables, you walk the streets wondering, where to go? Piano Bars. Those venerable New York institutions which have filtered down through time and geography, undergoing various metamorphoses along the way but still providing good music and good times, do indeed exist, right here in our own back yard. Washington can now boast a variety of clubs, lounges and sing show-tunes along with other week- end revelers, sit back and listen to good, traditional jazz, or even catch an occasional Chopin Etude if you're there on the right night and the piano man is in the right mood. To find out where to go for music tho suit the mood, read on.

CHARLIE'S OF GEORGETOWN 3223 K Street NW. 298-5985. Charlie's is known around town as a jazz club featuring top-name stars in the business, but for the price of a few drinks you can spend an evening in the front room listening to pianist Bob Diener accompanied by vocalist Annette Lowman. Starting off the evening with "Surrey with the Fringe on Top," Bob continues with a variety of show tunes, popular songs and jazz classics, playing what his audience wants to hear. "Summertime" as a waltz? "I'm Getting Married in the Morning" as an Irish jig? Bob is innovative and good, and takes pleasure in pleasing people. Bob and Annette together project a contagious exuberance. You can sit around the piano and join in "New York, New York" or relax in a dim corner; wherever you are, you're part of the show. Ask for "Easy Street," a favorite of Bob's, and you will leave feeling as if you didn't have a care in the world. BOB AND ANNETTE AT CHARLIE'S: Sunday through Thursday (except Monday), 9 to 1. Friday and Saturday, 9 to 1:30.

CAFE DE ARTISTAS 3065 M Street NW. 338-0417. A short walk through Georgetown will take you to the Cafe de Artistas, a friendly art gallery cum cafe with an international flavor and which is now coming into its own as a Washington jazz establishment. On Tuesday nights, come down to the Cafe de Artistas to hear Herbie Banks. A Grand Old Man of Washington jazz, Herbie pounds out boogie and blues without tricks but with great feeling, in the best New York piano bar tradition. Herbie loves to play, and derives great pleasure from his audience's appreciation of his music, so let him know what you want to hear. Whether he plays Dixieland jazz, a Gershwin medley, or a Beethoven Sonta, Jerbie plays to please. Thursdays and Saturdays, Larry Neeck brings jazz of a different flavor to the Cafe, blending bossa-nova and Latin influences with Miles Davis, Chick Corea and Willie "the Lion" Smith. New York? Paris? Rio? Close you eyes, sit back and listen to the music, mingled with a variety of foreign accents, and you could be almost anywhere. HERBIE BANKS: Tuesday, 8 to midnight. LARRY NEECK: Thursday and Friday, 8 to midnight.

THE FOUR SEASONS HOTEL 2800 Pennsylvania Avenue NW. 342-0444. Still in Georgetown, stop off at the Four Seasons Hotel. On Monday and Tuesday nights from 8:30 to 12:30 and all during the week from 4:30 to 7:30, Louis Scherr plays in the beautiful Garden Terrace. During the cocktail hour, Louis plays almost exclusively classical music. At night, joined by Tim Eyerman of the East Coast Offering on a variety of wind instruments, Louis turns to jazz, all kinds. One night, Louis and Tim might play various suites for jazz piano; another time, it's an evening of Keith Jarrett, always interspersed with such favorites as "Ain't Misbehavin' " and "When Son music sets him apart as a Washington musician. Side- stepping the main-stream and modern jazz scene, Ron plays the wonderful 30's and 40's songs by Porter, Gershwin and Rogers and Hart, bringing to Washington audiences a music they can rarely hear other places. For many, an evening with Ron Smith is an introduction to a world of music and mood which they have not yet experienced and to which they find themselves returning. When Ron starts to play, the din of multiple conversations gradually subsdies anmd people willingly let themselves be drawn out of their discussions to listen to the music. Ron's playing is anything but imposing; it is rather the gentleness and the authenticity of his feeling for his songs which captiviate the listeners' attention. An evening with Ron Smith is a gracious musical interlude which leaves one hungering for more. RON SMITH: Wednesday, Thursday and Sunday, 8 to 12:30; Friday and Saturday, 8 to 1:30.

THE WEST END CAFE on New Hampshire NW, between Washington Circle and L Street. 292-5390 A short stroll down Pennsylvania Avenue will take you to the West End Cafe, an amiable establishment providing quality entertainment for people wanting to eat, drink, or both. Burnett Thompson brings his years of classical training to the West End, so be prepared for a delighful surprise when you spend an evening there. Although Burnett usually plays solo piano, he is ofter joined by other musicians, classical and jazz alike. One might might feature a suite for flute and jazz piano a la Jean Pierre Rampal and Claude Bolling. Another night you might be greeted by the delicate notes of a Kreisler or Haydn salon piece, or a Brahms sontas, when Burnett is accompanied by violinist friend George Marsh. Friday nights are a special treat at the West End Cafe. John Previtti, bass player, frequently joins Burnett for what often turns out to be a spontaneous jam session, a lively combination of musical wit, humor and talent. The atmosphere at the West End is very pleasant. The joviality among the staff spreads quickly to the customers and one immediately feels welcome. Eric, the bartender, remembers your drink the second time you come in, the waiters greet you by name, and it is the kind of place where everyone leaves knowing everybody else. BURNETT THOMPSON: Tuesday through Thursday, 7:30 to 11:30; Friday and Saturday: 7:30 to midnight.

THE EMBASSY ROW HOTEL 2015 Massachussetts Avenue NW. 265-1600. If you are in the Dupont Circle neighborhood, stop off at the Embassy Row Hotel to hear Ron Kramer. Ron has been described as a pianist who can play any kind of music to any kind of audience. In the spacious Atrium Lounge, one can comfortably nestle back into cane back chairs, take pleasure from the fresh flowers on the tables and enjoy a blend of bossa nova, jazz and popular tunes. Ron doesn't feel that his music has to be the center of attention, and considers his playing as supportive to whatever the audience wants to do or feel, but it is so pleasant that one is quickly drawn into his playing. He believes in sticking fairly close to original arrangements, but he wooes his public by his personal charm and musical versatility, presenting them with something even better. Ron takes requests, so the mood in the Artium varies accordingly. One part of the evening will feature a show-tune sing-along, another will be more introspective and mellow as Ron plays Kenny Rogers, Billy Joel, or some melancholic country- western song. But whatever the mood, it is always pleasant. RON KRAMER: Monday through Saturday, 8:30 to 12:30.

THE FAIRFAX HOTEL goes because they know they will hear a good jazz piano, and first-time listeners quickly become regulars. John plays to the mood of his audience, and takes requests ranging from a Beatles' medley ot Cole Porter, touching on such jazz popular favorites as "Django" or "Have You Seen Miss Jones?" Under his masterful touch, even the muchabushed "As Time Goes By" becomes the most romantic of melodies, brining couples to their feet in the quieter corners of the lounge. For a hauntingly beautiful song, ask John to play "A Nightingale Sang in Berkely Square," a British WW II song and a guaranteed delight. JOHN EATON: Monday through Saturday, 9 to 1.

THE HAY-ADAMS HOTEL 800 16th Street NW. 638-2260. An evening at the Hay-Adams is a reminder of traditional Washington elegance. Walk into the dark wood-paneled cocktail lounge, sit back in a comfortable chair next to an open fire or join in around the piano with Judith Kenez. "Take away my piano and I can still entertain -- in five languages" she says with a laugh. Her repertoire is popular and classical, spiced with Russian folk music, French love songs and Latin rhumbas that she punctuates, in true cabaret fashion, with greetings to the audience, personal remarks, and a running commentary on life in general. Judith loves a vocal reaction from her audience, so don't hesitate to sing along with her, or ask for your requests; you may get more than you bargain for. A call for Cole Porter elicited "Begin the Beguine" intertwined with a Chopin etude, and at the mere mention on "something French," she presented the best of Edith Piaf a la unique Judith Kenez. From "My Fair Lady" to "Fiddler on the Roof", from Chopin to Bach, with Judith music becomes a universal language of entertainment and humor. JUDITH KENEZ: Monday through Saturday, 7 to midnight.

LENNY'S 1025 Vermont Avenue NW. 638-1313. Lenny's is a new restaurant-bar that has created an atmosphere of "formal informality" for those wishing to stop by for a drink or enjoy a good dinner. Lovely dining rooms and good food, a gracious greeting and courteous staff -- other places have these, but they don't have Michael classically trained, he was greatly influenced by the New York cafe society, and his versatility sets him apart. He intersperses his sets with jokes, greetings to the customers (many of them regulars) and comments about his songs: mood pieces, ballards, popular tunes and jazz. On occasion Terence will play a few of his original compositions. Ask for "Blossom Awaited," written with Washington in mind, lean back and smell the cherry blossoms on a warm spring day. MICHAEL TERENCE: Tuesday through Saturday, 6 to 11.