George Shearing used to be known as the great popularizer in jazz.

In the 1950s, he probably introduced thousands of neophyte listeners to the mysteries and beauties of jazz, and they went on to appreciate more esoteric musicians.

"I'm never offended by being called a popularizer," the pianist said softly in an interview yesterday at the Showboat Lounge in Silver Spring, where he's appearing this week through Saturday. "I'm not concerned about playing enough jazz - I'm more concerned about playing enough piano."

The sound of his various groups - a warm blend of piano, guitar and vibraphone backed by bass and drums - admittedly has had a degree of commerciality and wide appeal, he said. But the selling point is diversification, he added, pointing to the variety of records he's made - with brass, woodwinds, strings or as accompanist for Peggy Lee, Nat Cole and Nancy Wilson.

"I love jazz," he said. "I have used jazz. But if my programs were weighted toward jazz, I'd lose my diversification."

Many listeners apparently still like the Shearing sound, which retains the same effortless, melodic quality that's characterized it for 28 years. The Showboat was filled the other night with longtime fans, most of whom probably first heard the pianist in the 1950s.

His program was a wide-ranging mixture. The quintet played jazz pieces such as "Senor Blues" and "Donna Lee" with moderate gusto. "Ghost of a Chance" was given a low-key, lyrical reading. Shearing played a light and airy version of "Kerry Dance" and a robust rendition of "Honky Tonk Train Blues." "Lullably of Birdland," he most famous composition, was performed partly as a canon.

The baroque style in which played "Lullably" demonstrates another facet of his musical activity - his great interest in bach.

Since 1958 Shearing has been performing with symphony orchestras. He started out concentrating on Mozart. Now the focus is on Bach.

"The more years I get on this old body of mine," he said, "the more satisfaction I get out of playing classical music."

Shearing is still an inveterate story-teller, lacing his sets with abundant patter. Asked how he comes up with so much material, he said, "I spent a lot of time around Milton Berie's waste basket - which is to say I steal of a few and I come up with some of my own."

The pianist said 1976 was the most active year of his career. At 57, he recently performed in 56 cities in 63 days, preceded by an 11-day engagement at Disneyland.

He also married anew in the last 18 months, and his wife, Eleanor Geffert, a former vocalist with Norman Luboff, has Shearing jogging and bicyling, pasttimes to add to his other frequent activities of playing bridge and reading.

Blind since birth, the pianist is an incessant reader of braille editions of newspapers, magazines and newspapers.

He's also just been commissioned by the Sacred Music Press to reharmonize some early American hymns in folios for organ and piano.

But he says he never forgets what a relative used to tell him: "Why should anyone work when he has the strength to lie in bed?"