The Cellar Door, the Georgetown nightclub that helped boost the careers of such stars as Linda Ronstadt, James Taylor, John Denver, Richard Pryor, Neil Young and Jackson Browne, was sold yesterday for an undisclosed sum to Washingtonians Paul Kurtz and Howard Bomstein. The new owners took over immediately.

Kurtz owns a pair of restaurants, the Lido di Venezia in Arlington and the Jour et Nuit in Georgetown; he also owned a now-defunct jazz club called Consensus. Bomstein, who has been going to the club since his teens, is president of the Bomstein Advertising Agency.

Jack Boyle, partner with Dave Williams in Cellar Door Productions, flew up from that company's Florida headquarters for the sale. Boyle, who began working in clubs as a Georgetown University undergraduate in the '50s, first bought the M Street club in 1963, when it was known as The Shadows. He sold it the same year and bought it back in 1970.

In the last decade Cellar Door Productions has become a highly successful concert promotion firm, booking concerts locally at the Capital Centre and Constitution Hall and at the Bayou, which they purchased for a reported $500,000 in January 1980. The firm also promotes concerts throughout the South, and own 1,000-seat Agora clubs in Virginia Beach, Tampa and Ft. Lauderdale. "We simply can't spend the time to run a small club any more," Boyle said last night. "We're gearing up for more, larger concert situations."

The new buyers indicated that they will retain the Cellar Door's basic format (a mixture of jazz, folk and rock), possibly bringing in some more name acts. There was some confusion as to whether they would be able to continue using the familiar name.

During the mid '60s and early '70s, the undistinguished gray building on the corner of 34th and M streets was considered one of the top three or four clubs in the country, but in 1978 its seating capacity was cut by fire marshals from 199 to 125, and the club has not been able to attract acts of the same quality since then.