YOU would think Cybill Shepherd would be obsessed with Martha Stewart by now,if only because the domestic diva ‘s continuing saga has yielded employment for Shepherd in two TV movies (so far). The newest of the two,”Martha

Behind Bars,” which tells the story of Stewart ‘s trial on insider trading charges and her subsequent incarceration,premieres this week on CBS.The first one, “Martha Inc.,” a campy chronicle of Stewart ‘s rise from small-town caterer to America ‘s best-known homemaker,premiered on NBC on May 19,2003.

Truth be told,Shepherd,55,does not spend her waking hours wondering if some new and spectacular event will befall Stewart,and lead to yet another Martha movie.

“I guess I ‘m not obsessed with Martha,” Shepherd realized in a phone interview from Los Angeles,after mentioning that she has not yet checked out Martha ‘s new daytime talk show and has no plans to sample her new version

of “The Apprentice ” on NBC.

However,Shepherd does keep up with Stewart ‘s life just enough to know that Stewart herself said a few weeks ago that Shepherd would be welcome on her daytime show.”I think it would be fun,” says Shepherd..”I think it would give her great ratings too.”

The two have met only once, and that was “seven or eight ” years ago,Shepherd surmises, long before the former model and star of movies such as “The Last Picture Show ” and “Taxi Driver ” was asked to play Stewart on TV.

“It was a business situation – it wasn ‘t social,” Shepherd recalls, “and I remember thinking at the time,Boy,I ‘d love to play her.”

Shepherd couldn ‘t say if she would play Stewart a third time if the opportunity arose.Odds are, though,Shepherd would say yes, since she does find Stewart to be a fascinating character.

“I have more admiration for her than ever before after doing the second movie,” Shepherd said.

“This woman ‘s been through a hell of a lot.”

MARTHA BEHIND BARS

Sunday, 9 p.m., CBS