BREAKING UP IS HARD TO SELL

The end of an on-set romance is heartbreaking for the lovelorn, but it can be worse for the promotion department. When Brad Pitt and Juliette Lewis, a cooing couple for three years, broke up after making Kalifornia together, the change "made my life a living hell," says one marketing executive. The psycho-thriller, released Sept. 3, was to be launched with publicity infused with romance, but when the stars split, says the exec, "the best marketing ploy for this movie became null and void."

Not that a real-life romance always helps. The universally panned Wilder Napalm stars Debra Winger and Arliss Howard, who play a married couple in the film and have been quietly seeing each other off-camera as well. Too quietly for the film's flaks, who would doubtless prefer a more public movieland fling. "They are both single parents with young children," says a source from the set. (Hers is Noah, 6, his is Sam, 7.) "They'd plan a day off and go do something as a family." Predictably, neither Winger's nor Arliss' people would comment.

CAPITOL CUSTOMER

The opening fall episode of Sisters on Sept. 25 will find Sela Ward's fashion-designer character, Teddy, getting a surprise assignment from Hillary Rodham Clinton. "We thought it might be fun to jump-start her career with a phone call from the First Lady," says executive producer Ron Cowen. Mrs. Clinton nixed a chance to play herself in the show, however, saying she was too preoccupied with the Administration's health-care plan. Explains Cowen: "She's just a little busy to have her skirt hemmed on national television."

READY, AIM, REHEARSE!

As the late-night talk show wars heat up, boot camp is over for the casts and crews who have been taping dry runs in preparation. "It's to work out the kinks and find what works," says an NBC spokesperson. Veteran David Letterman, who launched his new CBS show-last Monday, did two dress rehearsals, while Chevy Chase, whose show on Fox start this week, did five mock shows, and Conan O'Brien taped 10 run-throughs to prep for his Sept. 13 premiere on NBC. For the record, Jay Leno did only two practice runs when he look over NBC's Tonight Show from Johnny Carson last year.

NIL NISI BONO

Seeking a writer to ready a script based on his autobiography, And the Beat Goes On, for next year's Fox miniseries. Sonny Bono is releved that he hasn't heard from Cher's lawyers. Yet. "There's no negative, which I expected," he says, adding that He thinks Cher is still holding a grudge. "We should be friendly," he says. Who'd he like to see play him? Sonny jokingly suggests Tom Cruise or Kevin Costner. And Cher? "Roseanne Barr," he cackles.

Mitchell Fink is on vacation.