MARY TYLER MOORE isn't acting her age, a fact that's agonizingly apparent in the gigantic opening close-ups of "Just Between Friends."

Moore joins the Peter Pan-theon of stars who don't want to grow up. She won't be the first or the last star who can't quite confront the passing years, but she's always seemed such a sensible gal.

She clings to the kittenish characterizations she established for decades-old TV roles in this made-for-the-movies drama from MTM. Come on, Mare. New wrinkles are showing; unhappily none of them in the acting department.

Moore plays a housewife named Holly, but she might as well be Mary Richards with a husband (Ted "Cheers" Danson) and a couple of teenage kids. Her girlishness contrasts weirdly with her drawn face here, and it doesn't help that Danson looks at least a decade younger than she does. (There's no hint that she's supposed to be older -- a la Alexis Colby.) An older partner would have gone a long way towards resolving the casting incongruity, as would a soft-focus lens. To her credit, Moore doesn't hide behind one.

As Holly, she goes from dependent wife to independent business owner via a friendship with Sandy, a confident TV reporter and fellow sweat-setter at a Pasadena spa. After their friendship grows, they discover that they have more in common than a passion for aerobics fitness: They are sharing the same man -- Holly's hubby, an earthquake expert who makes the earth move for both of them. Of course they find out only after they've opened an exercise studio together. Then Sandy becomes pregnant in this sudsy scenario that plays a little like "Perfect" meets "Micki & Maude."

Moore, flouncing purposefully about in her teensy leotards, proves that indeed you can be too thin. Otherwise her performance is the usual, the one we've come to expect: coy, confused, flustered, unable to cope.

Danson hasn't developed his character much beyond the Aramis man. But costar Christine Lahti is excellent as the hardnosed Sandy, with Sam Waterston completing the quartet in a warm role as the family friend.

The story is directed by MTM vet Allan Burns who offers a middle-class, middle- ground exploration of infidelity and female bonding with a convenient solution. Naturally, the philanderer is nearly enshrined by the two women who come to understand that he was just a good guy who was misunderstood.

JUST BETWEEN FRIENDS (PG-13) -- At area theaters.