Big Nick Nicholas took off his coat and tie in the middle of playing a medium groove Charlie Parker tune.

The One Step Down, Washington's newest weekend jazz emporium, was hot and funky, and the tenor saxophonist was blowing hard. A mostly young crowd was with him on every note - in the fluid, sweet version of "Invitation" or the Latin-rhythm-punctuated "Manteca."

This kind of inspired scene is becoming familiar every weekend at the One Step, a long, narrow shotgun-shaped room at 2517 Pennsylvania Ave. on the edge of Georgetown.

The One Step has leaped into the void left when Harold's Rogue and Jar closed in January. For the last four months the club has booked "little" name performers like tenor saxophonist Charlie Rouse, vocalist Earl Coleman and pianist Joann Brackeen for weekend appearances. Local pianist Mare Cohen plays on Monday nights.

The rest of the week the 75-seat club reverts to what it has been for 16 years - a neighborhood bar boasting the hippest jazz jukebox in town.

Owner Joe Cohen says he decided to go with a live music policy after re-modeling the club several years ago. At first, he only had Monday night jam sessions. Then along came Ann Mabuchi, a recently divorced mother of two who plays piano for her own pleasure and dreams of someday opening her own club. Mabuchi now handles the bookings and plans to present a diversity of artists appealing to various age groups.

Right now most of the club's customers are in the 21- to 30-year-old group, including healthy smattering of student-types.

It didn't matter that most of them hadn't been born when Nicholas first made his name. The saxophonist captivated them anyway. Known to his closest relatives as George Nicholas, Big Nick soared on "Autumn in New York" and "Lover Man."

Like many jazzmen of his generation, Nicholas, 59, doesn't play his horn, he sings and delivers an eloquent rap. His rendition of "What a Wonderful World" came out in raspy. Louie Armstrong type tones, while "As Time Goes By" was honeyed and romantic.

The weekend Washington appearance was rare for Nicholas.Recently, he's been working at a country club in Charlottesville and as a music consultant for the public schools in that city, touring only occasionally.

Mabuchi and Cohen were pleased to have him. The live jazz policy is beginning to catch on, Mabuchi says. In upcoming weekends she has schedule Lee Konitz and Gary Bartz. CAPTION: Picture, Big Nick Nicholas, by Fred Sweets