'Signature' on CBS Cable

What new TV program manages to be traditional and innovative simultaneously?

Despite all the boasting about cultural programming on cable channels, one of the most excitingly innovative programs to emerge on cable is what may on first glance seem to be a traditional interview show - ''Signature.'' It is on the air a half-hour each weekday on CBS Cable, viewed by more than 3 million cable subscribers on more than 300 cable systems.

The format of ''Signature'' is so simple that it seems almost like a nonformat interview. The guest sits in a comfortable chair with only a brick wall behind him while the camera circles constantly, coming in for tight shots, extreme closeups, long shots from just about every possible angle. You can see the uneasiness and bravado in the eyes. Even when the show goes on the road, as it does occasionally, the set remains that familiar, undistracting brick wall.

The interviewer is never seen - he serves as almost an alter ego, the voice of conscience, the self-questioning uncertainty or certainty of the guest himself.

Producer of ''Signature'' is Dolores Danska, director is Michael Albanese, and executive producer is Gregory Jackson. Together they have managed to take an old form and give it new style and great substance. Although sometimes the voice of the interviewer may seem a bit familiar, the producers of the show insist on maintaining the anonymity of the questioner.

Interviewees are chosen with an eye for current relevance as well as general interest, and in recent weeks have included Peter Bogdanovich, Max von Sydow, Jason Robards, Diane von Furstenberg, Martin Sheen, Cliff Robertson, Joseph Levine, Thor Heyerdahl, John Irving, John Simon, Raquel Welch, Robert Evans, and tonight (Friday) Benny Goodman. Next week will feature Glenda Jackson, Steve Allen, Louis Malle, and Roberta Peters. Many guest stints are repeated.

Thor Heyerdahl, who has sailed the world many times on rafts and strange vessels, admitted on the show that he doesn't know how to sail a normal sailing boat.

Lots of unexpected things happen despite the tight format. Fashion designer Diane von Furstenberg became angry when her new perfume was not pictured on the show. She claimed to have been mistreated by the media.

CBS Cable, an advertising-supported service that is transmitted free to basic cable systems, seems to be the most well-rounded of all the cultural channels. If your system does not get it, you could call the president of your cable system and ask for it.

''Signature'' gives new life to an old form. It permits important people to sound off, to pose, to evade important questions, to present themselves straightforwardly . . . at their own risk.