It's late afternoon on a balmy L.A. day and Jane Fonda and Jennifer Lopez are having a catfight.

"Ughhh! Get off me!" Lopez shrieks. Fonda does just the opposite.

Finally, the two fall to the floor with a thud.
A beat.
Then: That famous Fonda laugh. Deep, throaty.

It's just a movie.
Fonda and Lopez are filming "Monster-in-Law," which is being helmed by Aussie director Robert Luketic, on the Culver Studios lot. In the film, Fonda plays Viola Fields, a broadcast newswoman and mother thrown into turmoil when her television show is cancelled. Lopez plays Charlie --- short for Charlotte --- a fledgling fashion designer who has growth written all over her. ("Charlie is faced with the challenge of pushing beyond her personal limitations and boundaries," read the production notes.) She also happens to be engaged to Viola's son, which is where the monster part --- and the fun --- begins.

The film is Luketic's third Hollywood feature after 2001's "Legally Blonde" and this year's "Win a Date With Tad Hamilton!" and his first with a high eight-figure budget.

"I feel grown up," the 33- year-old says of being given the reins to "Monster-in-Law," which he characterizes as being in the $60 million range. ("Legally Blonde" was made for $17 million.)

"Monster-in-Law" is also Fonda's first movie in 15 years. She was last seen in 1990's "Stanley and Iris" opposite Robert De Niro (news), before retiring into a mix of trophy wifedom and philanthropic activism with then-husband Ted Turner in 1991. For her part, Lopez is coming off the train wreck that was "Gigli," and "Jersey Girl."

In other words, all three need a hit, which could have added an extra burden to proceedings already marked by rumors of diva-like behavior from the two stars off-screen.

"I can honestly say to you, on the record and off the record, it never existed," Luketic says.

Fonda disputes the rumors herself several days later via cellphone. "Jennifer and I got along very well," she says. "She's a very smart and talented woman. ... We have something in common in the sense that I wasn't just about movies: I produced and had the workout business and I had politics, and she has movies and music and clothes Maybe she can be (a diva), but she wasn't on this film."

On the set, matters are less clear-cut. Luketic stays remarkably relaxed as Fonda yells from the room where the cat fight is taking place, "You're getting what you need, right?!"

Suddenly, she appears next to him and watches the playback herself. Up close and in a nearly-backless dress, she is remarkably trim and fit --- a Platonic ideal of her 66 years, and looking nearly 20 years younger. "What was wrong with that?" she asks.

Luketic follows her back into the set room, and confers with his actress. The next time around, the take is short --- and Luketic jumps up with delight. Chris Bender, whose company Benderspink is one of the producers of the film, smiles and explains that such enthusiasm is a Luketic trademark. "Usually, he springs up, practically does a back flip," Bender says.

Lopez soon appears and checks out the monitor herself. "She must be cranky, 'cause I'm cranky," the multi-hyphenate says of her co-star.

When a wardrobe attendant tries to undo a button on the back of Lopez's dress, the actress reaches back only to have her hand gently patted away. "Can't I scratch myself?" she snaps. Moments later, Lopez walks back to the set and the woman scrambles to hold her dress up off the floor.

If Lopez has been a tabloid lover's dream as of late, the return of Fonda --- a two-time Oscar winner and the bluest of Hollywood bluebloods --- has emerged as this project's calling card.

"I had no desire (to return)," Fonda says of Hollywood. "I didn't miss it. But I am a very different person than I was 15 years ago, and I was curious about how that would translate to the screen."

While she had been offered other roles, Fonda says she "wanted to do a comedy," citing 1977's "Fun With Dick and Jane" as another light picture that was successful at a crucial point in her career.

One might conjecture that Viola's predicament also is on point for Fonda, who separated from Turner in 2001.

Paula Weinstein, another of the film's producers and a friend who's known the actress since they met as fellow protesters at the Republican National Convention in 1972, explains her character: "She's playing a successful woman at a moment in her life when the outside world is no longer paying all of its attention to her. She's letting go of everything."

Fonda seems to be in the mood to move forward, and have a good time while she's at it. "I don't want to work if it's not fun," she says at one point. Indeed, she could be talking about her life aims as much as the film when she says of life on "Monster-in-Law's" set, "It was fabulous fun. ... It was kind of like playing in a sand box."

The actress is cagey, however, about any plans. "I'm not thinking in terms of trying to rebuild a movie career," she says. "I don't want to make a whole lot of movies."

The actress notes she is penning her memoirs for Random House, which will keep her busy for the next year anyway. "But then again, I didn't think I'd do another movie again (before 'Monster-in-Law')," she says.

Hits Cinemas Summer 2005