EVEN NEIL SIMON has heard the word. In androgynous '85, it's "cross- dressing." And this prolific playwright was never one to pass up a profitable trend.

So it's simple -- Simon says "switch the sexes," and back to the boards bounces "The Odd Couple," with Rita Moreno as "Olive" Madison and Sally Struthers as fussbudget "Florence" Unger.

It works. Directed with low-key flair by Danny Simon (Neil's brother), the durable "Odd Couple," in for four weeks at the National Theater, remains a friendly and familiar farce about sharing lives and living rooms.

Simon has "updated" with a light touch, and one shouldn't go expecting a feminist message -- in fact, the playwright seems to consciously avoid that. The world has changed since 1964, and Simon notes the changes quietly, without belaboring the point, sprinkling in a few brand names and a nod to '80s mores.

Though they've crossed the gender gap, Simon's characters have remained true to their natures. Divorced Olive (she's paying alimony to her out-of-work actor husband) is happy in her homely home till Flo, dumped by her exasperated husband of 14 years, shows up at the door with her bag of tics.

Moreno's earthy Olive is still a human dust magnet, a girl who just wants to have fun, and Moreno is a hoot, with her dry-voiced, teeth- clenched take on Walter Matthau's classic exasperation. Struthers, who made neurosis an art as Gloria in "All in the Family," is perfect as the intensely irritating, compulsively clean Florence, a yuppie princess, with her wind- tunnel sighs and "low threshold for composure."

As with any Simon play, the details and reactions are often funnier than the polished punchlines. David Mitchell's good-looking set is apartment-verit,e, down to the fingerprint smudges on the putty-colored walls. The evening is helped tremendously by the solid supporting cast. The four poker pals are superb Manhattan characters, particularly Marilyn Cooper, as the sweetly oblivious Vera. Lewis J. Stadlen and Tony Shalhoub are handsome, hapless and hilarious as the Costazuela brothers, who replace the original's Pigeon sisters as Flo and Olive's disastrous dates.

THE ODD COUPLE -- At the National Theater through February 17.