Blair Brown throws open the door of her dressing room et voila! - the pale blue dress she has just taken off is standing upright on the floor as if someone were still in it.

"It's been a long time since you wore clothes that could do that," Brown says of the polyester frock, her attire for a '50s sitcom dream sequence in an episode of The Days and Nights of Molly Dodd (6:30 p.m., LIFE, cable-TV) being filmed on a soundstage in Astoria, Queens.Thirteen new episodes of the offbeat comedy-drama that left NBC last summer begin airing on the Lifetime Television cable network tonight.

In the episode being filmed, the 12th of the 13, Molly thinks she might be pregnant, but isn't sure which beau is the father. In the dream sequence, Molly is a sitcom mom, flitting from TV to baby carriage to kitchen, serving the demands of three undershirt-clad husbands: bookseller Moss Goodman (David Strathairn) turned construction worker, black detective Nathaniel Hawthorne (Richard Lawson) as grocer, and doorman Davey (James Greene), still a doorman.

The cast is the same, the look is the same, but it's a big jump from the No. 1 network to a small cable channel.

"If one more person comes up to me on the street and says, `I love your show. When is it going to be on again?' or, `I love your show, but I don't get cable,"' Brown said with a sigh. "I mean, I feel we're a little early in that sense for cable. I bet in a couple of years this will all be very different.

"It's really disheartening, that, because you think, well, our work is better this year and yet fewer people can possibly see it."

Nevertheless, she and producer Jay Tarses are happy enough just to be in production.

"They've been unbelievably nice," Tarses said of Lifetime. "I mean, they want us. They make us feel as if we're the answer to whatever prayers they have, and it's a terrific feeling to not feel like somebody's stepsister. At NBC, they just kept putting up as many obstacles as they could hoping someday we'd trip over one, and eventually we did. Lifetime just wants us here. They're happy we're here."

The series did well in the ratings and received raves from critics when it first appeared as a spring replacement on NBC in 1987. The premise was simple: Brown as a divorced New York woman struggling with an irresponsible ex-husband, a fretful mom and a nonexistent career. It wasn't "Mary Tyler Moore."

NBC didn't bring the show back until the following spring, and then it got a slot in the boffo Thursday comedy lineup following "The Cosby Show." When it landed only in the top 20 instead of the top 10, it was moved to another time period where its ratings dwindled before it was canceled.

Lifetime, which caters to female viewers with health and lifestyle shows and reruns of such series as "Cagney & Lacey," picked it up last summer, and Tarses moved the production from Los Angeles to Queens.

"We figure next year we'll be working offshore," Brown said, laughing. "We'll be the first offshore television show outside the 20-mile limit shooting on a boat and sending it back, because they can't get rid of us, try as they may."

Ironically, she noted, the show is now shot on a soundstage next door to "The Cosby Show."

Tarses had complained, at times bitterly, about the way "Molly Dodd" was treated by NBC Entertainment President Brandon Tartikoff, who thought it too weird for a mass audience.

Tartikoff stopped by the set recently and joked that he was announcing a network pickup. Tarses shrugged. "I like him," he said. "He's got a job to do. His job is to be No. 1."

Tarses will find out in May if Lifetime wants to continue the costly production of "Molly Dodd." If not, he's reluctant to return to a network. "Never's a long time," he said, "but I hope I don't have to go back and do that again. I'm willing - if they give me a 66-show commitment."

The split with NBC wasn't necessarily permanent, even if it did get a little vitriolic in the press. Tarses does have an in at the network. His daughter, Jamie, is director of comedy development.

"I did say I wasn't going to do anything for a while, but they'd be crazy not to come back to me," said Tarses, with a grin. "I'm a genius."

-Elsewhere in television:

LIFE, OR AT LEAST HIATUS, IS A CABARET - Now that CBS' "Designing Women" has wrapped for the season, star Dixie Carter is performing in cabaret at the Cafe Carlyle in New York through April 29th. Her repertoire ranges from Rogers and Hart to Cole Porter, to Laura Nyro, Bruce Springsteen and Bob Dylan.