Jazz and nostalgia piano fans of diverse tastes can find keyboard action to their liking within a six-block spread of Alexandria's Old Town. A recent Saturday evening of pub-hopping turned up a senior member of the be-bop school, a younger modernist, a mainstreamer, a scholar of ragtime, a vaudeville showman and a barroom sing-along type.

John Malachi, at the 219 Restaurant (219 King St.) Fridays and Saturdays, was a key member of the Billy Eckstine orchestra of the 1940s. The room in which he sits, professor-like in his dark suit with coat hanging open, is an upper-crust Victorian living room with its large Edwardian portraits, coat of arms and skylight. From the mezzanine above, Malachi's large hands are dark against the white keys as they deftly construct a blue-tinged "Summertime." A patron leans over him and whispers a request in his ear, dropping a bill onto the propped-open grand piano. Conversation is unbroken at many of the small, dark wood tables, but some sit in silence, either lost in their thoughts or seized by the pianistic mastery of this black man of serious expression who rarely consults the bulging briefcase of sheet music resting against a piano leg.

A block away the large, brick-wall, upstairs room at Il Porto Ristorante (121 King) is humming with the chatter of pizza eaters and beer drinkers at the red and blue checkered tables. Johnny Maddox (formerly 'Crazy Otto'), a poster-sized photo informs, has sold 11 million records and has "his own star on Hollywood Boulevard." Maddox, in striped shirt, black bow tie and vest, stands with mike to mouth and introduces Euday Bowman's "Twelfth Street Rag" with the the observation "He never made a dime of royalties out of it." He takes his seat, and his hands, seen in the angled mirror suspended above, are immediately careering around the hairpin curves of the familiar tune. His virtuosity is regarded with a scattering of applause and the balding pianist is off and running with a medley of Scott Joplin numbers. Maddox is on hand Monday through Saturday.

A few doors away two pianists work the Fish Market (105 King). Buck Kelly, in the Ship's Lantern Lighted Back Room, is a Gay Nineties replica in sleeve garters, red bow tie and waxed handlebar moustache. He rocks from side to side as he roars down the rails on "Chattanooga Choo-Choo" and then sings a jaunty "Ain't Misbehavin'." A fan requests some Irish music and sails a dollar bill paper airplane down the piano bar into the beer schooner kitty. W.C. Fields, as the Bank Dick, leers cynically from a poster as a sing-along gets under way to "Wild Irish Rose."

Upstairs the decor is equally nautical and the crowd livelier in the Captain's Lounge, a large room that attracts the young with a sprinkling of older admirers of the show tunes and pop songs of yesteryear that compromise much of the repertoire of Steve "Stubby" Heist. The portly, ever-smiling Heist lifts many in the crowd to their feet, beer mugs aloft, to sing a rousing "Oklahoma." Hardly have they taken their seats when he is pounding out "Flight of the Bumble Bee Boogie Woogie" with a "Look, Maw, no hands" grin. His audience looks on in awe. Kelly and Heist work Monday through Saturday.

Around the corner at King's Landing (121 S. Union), elegance is the word in the upstairs King's Loft with its long bar, hanging potted plants, metal fountain sculpture and soft light. Pianist Tony Matarrese peers over his broad shoulders at the lounging patrons who are deep in talk and, almost without exception, unmindful of the complex harmonies rolling off his fingers as he interprets jazz standards and works in an orignal composition or two. He is at the piano Tuesday through Saturday.

It is about midnight and the Henry Africa restaurant is crowded with standees several deep at the bar. Vivian Scott, a Howard University and Juilliard graduate, is swinging "Sentimental Journey" with bassist Jim Ford as her accompanist. Ford disappears for a brief break and Scott remains on her bench staring absently at the crowded tables until a man, drink in hand, sits beside her. She cocks an ear and, in apparent answer to a request, nods. Ford is back at his big bass in a few minutes and the two, oblivious to the considerable noise level of the late evening drinkers, are into a medley of Ellington tunes. A man across the room turns his head from his partner's and raises his glass to the pianist. A fleeting Mona Lisa smile is her response and she recedes into her music. Scott and Ford are there Tuesday through Sunday.