BETTY WHITE: "John, the CBS brass just called." John Hillerman: "Good, they've learned how to dial."

This could be real life, but it is just a rehearsal for an episode of "The Betty White Show," a new CBS sitcom from the MTM factory premiering Monday at 9 p.m., on Channel 9. White, who won an Emmy and spent four years playing the over-sexed Sue Ann on "The Mary Tyler Moore Show," now plays a TV actress whose new series, "Undercover Woman," is being directed by her ex-husband, played by John Hillerman.

And so on the "Betty White" set - in MTM studios over the hill from Hollywood - there are two sets of imprinted cast and director's chairs, one for "Undercover Woman," to be used on the air, and one for "The Betty White Show," where the real conferences and rhubarbs take place.

Except that people around the "White" show say there are no rhubarbs because everybody just loves Betty White. "If you can't get along with Betty White," says Hillerman in his smooth Givenchy voice, "then you really are in trouble."

The series is expected to be a winner. When you tell White that she exclaims, "Oh, it again! Hold the thought Oh, God!" And Hillerman asks, "Is there any wood left in the world?" so that he can knock on it. What the program has going for it is the MTM touch, which includes high caliber comedy writing, and its two costars, whose cat-and-mouse tiffs can be extremely funny.

"MTM came to me and said they wanted to do a show with me," White recalls, sitting in a small dressing room between takes. "We all agreed it should not be the Sue Ann character again; she's a good hit-and-runner, not a sustainer. So they had several ideas. The first was that I be a nun in a girls' school - Sister Scholastica, who's always in trouble with the church. I said, 'I don't think so.'

"Eventually we settled on an actress doing a TV series. I thought it would be fun if the show within the show were a space family thing, like a Star Trek' or something, because I'm a space buff. They said okay and I went home thinking that was that. Two weeks later they called me and said they were ready to take the scripts over to CBS. And they said, 'Oh, we changed one little thing: You're a policewoman." She laughs and gives her listener a little poke in the arm.

White's Sue Ann was an especially satisfying triumph because she seemed to be lampooning the very happy homemaker image she'd cultivated in years of TV comedies, talk shows and commercials.

"Oh, I loved doing Sue Ann. They said, 'We need a Betty White type' when they wrote it. I thought it was great because there's more SUe Ann in Betty than there is whatever that image is of Betty, and it was great fun to be able to pull out all the stops and not have to worry about it. The new character I play has overtones of Sue Ann but not quite as much promiscuity. There's bitchiness, but with the new character, she doesn't strike first. She waits until somebody else strikes and then she lets 'em have it."

The old Betty White image was fostered by such TV sitcoms of the '50s as "Life With Elizabeth" (1953-55) and "A Date With the Angels" (1957'58). White was as wholesome as Wonder Bread. Plot lines involved such raw realism as "Elizabeth's biscuits not turning out - that sort of thing." And although "Angels" was about two honeymooning newlyweds, "We never got into any sex jokes at all."

There were no bedroom scenes in the '50s. There were barely any bedrooms.

In the new program, the two ex-spouses spar regularly on the theme of who is more sexually inadequate than whom. In the opener White tells Hillerman, "The most romantic thing you ever said was 'Am I too heavy?' And that was when I was carrying you over the thresh-hold."

Says White, "We didn't worry about relevance in the early days. We were trying to be funny. We were more two-dimensional cartoon characters than three-dimensional real people."

Hillerman is doing his first weekly TV role after 17 feature films, frequent appearances on the occasional "Ellery Queen" series on NBC and seven generally glorious years at the late great Washington Theater Club, where he played almost every part known to man. This doesn't mean he is a snob who looks down on television.

"It's so powerful, you can't look down on it," he says. "If you want to be a star, it's not possible to put it down. I don't miss the stage at all. All that work, and no money! You can't make any money in the theater and that's one of the reasons I got out. When I left Washington I was 35 years old, I was a 'star' at the Theater Club and I had $750 in the bank. A star's salary on Broadway is a third of what I make in television.I didn't want to wind up as a broken-down broke actor."

Hillerman poo-poos reports from old friends in Washington that he "went Hollywood" soon after he got there and started making bucks in droves, but then he admits he acquired a Cadillac, a valet, a Jacuzzi, a new house, and a Video Beam projector for a screening room outfitted with push-botton black-out drapes. "Hmm, it is very Hollywood, now that I think about it," he says.

That doesn't mean he would do anything on TV for the money. He turned down a lot when producers sought him for a role in a series based on the "Blazing Saddles" movie. "It was an enormous amount of money, but they wanted me to play his dreadful character, a loud hick who was an idiot and got bested every week. I would have been miserable, so I turned it down, even when they kept upping the price.PS - they made the pilot with somebody else, it was a complete disaster and didn't sell."

Hillerman says he will enjoy playing White's ex-husband - a debonair, unflappble smoothie who rarely raises an eyebrow, much less his voice - because "it's very near what I really am, very near me as a person. I am pretty unflappable. I've been around a long time, I've been acting for 25 years, and it takes a lot to flap me. I'm very easy-going. I don't like strife in my life."

He speaks with the calm authority of an understanding shrink.On the premiere of the show, his ex-wife becomes so irritated with his cool facade that she tips a whole wall over on him after pummeling him with prop crockery. "And John didn't turn a hair," White marvels. "I got a little over-eager with the breakaway chairs, and it looked to me like I hurt him with one of them, but he insisted it didn't."

The two stars seem genuinely fond and appreciative of each other. "I adore John; I think he's going to knock everybody out," White says. Hillerman says White will give joke lines to other actors if she thinks they might get a bigger laugh with them."You don't run into that kind of thing very often. Betty is terrific, an absolute joy. She's almost too perfect - no, it's a joke. I love her and I think we can live very happily together if the show runs a long time."

By all rights "The Betty White Show" should be a hit, but in television you really never know. Really. Never. "It's in the lap of the gods," says White. "Let's put in this way," says Hillerman. "I'm not spending the money yet."