Just inside the Showboat Lounge the other night a man was asked if he had a reservation. "What do you mean - a reservation?" the man exclaimed. "Who need a reservation for Bill Evans on opening night - the only people that'll be here will be other pianists."

Unfortunately, that was just about true on Tuesday night. Nevertheless, the handful of patrons heard some of the most lyrical and harmonically rich piano being played today.

Evans, a poet of the instrument, has a special way with altering the phrases of a familiar piece, shaping it anew by slowing down certain passages and accelerating others. Under his hand, melodies seem clearer, more supple, as he plays notes in cliff-hanging suspension.

That's the way he performed Johnny Mandel's "Emily." Intrinsically pretty, the melody glowed even more under the Evans treatment, as did the breathtakingly lovely Francis Hime ballad "All Mine."

Evans' accompanists these days are bassist Eddie Gomez and drummer Eliot Zigmund. Gomez' work was particularly notable for the range he covered on his instrument and his melodic and rythmic interplay with Evans.

The pianist, who's held out against changing his music to fit the contemporary rock mold, nonetheless, is leaving Fantasy Records for Warner Bros. "They offered me a good deal," he said, "and I didn't want to turn it down."

Before leaving Fantasy, he has two recording dates to fill - one a trio date and the other scheduled next week, with Lee Konitz and Warne Marsh, the saxophonists who became prominent in the 1940s as students and colleagues of pianist Lennie Tristano.

Evans will appear through Sunday.