Updated July 07, 1997 12:00 PM

IN HOLLYWOOD—LET’S FACE IT—SHE HAS earned a reputation as a pretty difficult woman. Julia Roberts clashed with Nick Nolte during 1994’s I Love Trouble and created such a fuss making 1991’s Hook that the crew nicknamed her Tinkerhell. So when the actress grabbed a bullhorn at the end of one long, hot day of shooting her new hit movie, My Best Friend’s Wedding, in Chicago last summer, some coworkers braced themselves for a dose of divaesque behavior. Instead, Roberts called out “happy birthday!” to a crew member. “It was so cute!” recalls extra Bonnie Deutsch. “And then she turned to the audience, and she thanked them for supporting us and letting us tie up all the traffic. Everybody just thought that was wonderful. She said, ‘We just want to thank you. We know this is a hassle for you, but we’re thrilled to be here.’ ”

Even now, Wedding director P.J. Hogan remains amazed at how the 5’9″ beauty rubbed elbows with the City of Big Shoulders. “She was,” he says, “the hottest thing to hit Chicago since the fire.”

But Julia Roberts has always been hot. What’s new is the warmth that, from all appearances, pervades her personality. The woman who once had rocky affairs with Liam Neeson, Jason Patric and assorted other leading men has become a more serene and secure Julia, one very different from the reclusive star who took the part of Dr. Jekyll’s maid in the grim 1996 box office bomb Mary Reilly, then locked herself in her London apartment to hide from the paparazzi. Maybe she has just matured, but with her 30th birthday looming on Oct. 28, Roberts has been out and about more, making friends with strangers while walking her dog, dancing on the occasional New York City bar top and generally exhibiting an intriguing mixture of sanity and sass.

Roberts’s decision to do Wedding shows that after several years of increasingly questionable career choices (Mary Reilly, Michael Collins, Ready to Wear), she has learned to lighten up and return to the sexy, funny roles that turned the once-gawky girl from Smyrna, Ga., into a star. Pitching the film to theater owners at the ShoWest convention in Las Vegas last March, Roberts pleaded, “My hair is a lovely shade of red and very long and curly the way you guys like it; for the love of God, please see this movie!”

Roberts’s three homes—she has a duplex apartment in New York City, a 50-acre retreat in Taos, N.Mex., and a house in the Hollywood Hills—are calmer, happier places these days. One possible steadying influence: her mother, Betty Motes, whom she sees frequently. And two years after their March 1995 separation, her friendship with Lyle Lovett is closer than ever. As for her love life, while she hasn’t lacked for dates with handsome young swells in Manhattan and L.A., she has apparently rid herself of the impulsive streak that led to a hastily canceled wedding with Kiefer Sutherland in 1991 and a hastily arranged one with Lovett two years later.

Make no mistake: Roberts remains very much the Movie Star. She maintains a whippet-thin body (thanks to regular running, even when she’s facing 18 hours on a set) and pals around with industry players such as her agent Elaine Goldsmith-Thomas, who gets Roberts $12 million a picture. Yet the actress no longer plays the on-set prima donna. “Julia’s smile,” says Wedding costar Dermot Mulroney, “is like a thousand-watt bulb. Everybody falls for it, but there’s nothing like it when she smiles and laughs. You can’t help but be drawn into it.”

You don’t have to convince Officer Jim Meir, a 51-year-old Chicago cop whom Roberts met one morning while walking her 3-year-old German shepherd-husky mix Diego. Meier was offering T-shirts in exchange for donations to the Special Olympics, and when he showed her one, Roberts declined, saying that she didn’t have any money. She promised to come back the next day. “Yeah, right,” Meier recalls thinking. “But, lo and behold,” he says, “at about 11 the next day, here she comes, walking across the street”—with some $100 in cash. “She said, ‘I promised I would come back,’ ” Meier recalls, ” ‘and here I am.’ ”

This is the Julia that her fans have loved since her first major screen appearance, in 1988’s Mystic Pizza. The grace and charm, though, have been slow to come. Roberts became a superstar at an age when the average college kid is still picking out that first suit for job interviews. “Julia was a baby [then],” says Maggie Wilde, who was Richard Gere’s producing partner when Pretty Woman (1990) was made. “It’s a little unfair, people saying, ‘How come she didn’t stay 21?’ You know, like…how come she didn’t stay a virgin?” Still, Wedding producer Jerry Zucker says that, for Roberts, growing up in public has had a plus side. “Because she’s been in an adult world for so long and has had to respond to major pressures,” says Zucker, “she’s got a savviness and maturity that’s beyond her years. You expect her to be 40 now, like it’s time for her to play mothers or something.”

That’s a role Roberts isn’t rushing into. “If I’m married when that happens, terrific. If I’m not, well, that’s fine too,” she told London’s Sunday Telegraph. “There’s nobody in particular [in her life],” says a friend, “yet there are a lot of people vying for the opportunity.” Since her split from Lovett, Roberts briefly dated Matthew Perry for a couple of months early last year after her guest shot on Friends, which aired in January 1996. (“I love a man who can fax me five times a day,” she told him in a saucy note reported by Redbook.) After Perry, she went out with New York City celebrity fitness trainer Pat Manocchia, 35, for several months. The pair, says a source close to Roberts, are friends but no longer see each other exclusively. Lovett is once again a big part of her life, although he denies reports that they are an item again. “Julia and I are very close,” the singer says, “and we do see each other socially.” The two are often spotted in each other’s company, and Lovett has reportedly visited her at her spread in Taos—where she has tooled around in a 1965 VW bug. And he still calls her mother Mom. “[Julia and Lyle’s] relationship was based on something true and real,” says a friend, “and that will always be there.” Both Lovett and Manocchia attended the New York premiere party for Wedding on June 17, but Roberts’s escort was openly gay costar Rupert Everett, who plays her gay pal in the film’s star-making role.

At home in Manhattan, Roberts is “a cross between Martha Stewart and a bohemian beatnik,” says one pal. “She’ll invite you to her apartment for a home-cooked meal with homemade bread and turkey and all of the trimmings. Then you’ll sit around reading [poet] Pablo Neruda and discussing art.” Roberts even knits sweaters for friends and teaches needlework to colleagues such as Wedding costar Cameron Diaz. Her sister Lisa, 32, is one of her best friends, and she adores her 6-year-old niece Emma, the daughter of Kelly Cunningham, the ex-girlfriend of Julia’s actor brother Eric Roberts, whom Julia hasn’t spoken to since the two parents feuded over custody in 1993. Although Roberts’s mother, Betty, a real estate agent, still lives near Atlanta, Julia is devoted to her and gave her a blink-and-you’ll-miss-it, nonspeaking part as a brunch guest in Wedding.

Roberts’s one constant traveling companion, however, is Diego the dog. While she was shooting Wedding, he stayed at Chicago’s Citizen Canine, the swank doggy bed-and-breakfast where Oprah Winfrey sometimes keeps her six golden retrievers and two cocker spaniels. According to “innkeeper” Steve Malone, Roberts brought “regular old, basic dog food” for Diego—unlike some celebs, who request everything from Mexican eats to Chinese takeout for their pets’ pampered palates. And Roberts, says Malone, “waited in line like everybody else. She didn’t expect any star treatment.”

These days, Roberts is letting her hair down. Boozers at a Manhattan honky-tonk called Hogs & Heifers last September looked up from their long-necks to find her boogeying on the bar and shucking off her 34B Maidenform from beneath her shirt—in accordance with the establishment’s freewheeling tradition. On the set of Wedding she goofed with White Sox fans while filming a scene at Comiskey Park during an actual game. The beer-sodden spectators, recalls Mulroney, “were doing their level best to get Julia to raise her T-shirt. They were like, ‘Hey, Juuuulia! This Bud’s for you!’ Then they all raised their shirts and showed her their sunburned bellies.” Roberts just laughed and screamed back, “StairMaster!”

Wedding, which earned $21.7 million in its opening weekend, topping Sleepless in Seattle‘s record for romantic comedies, seems made-to-order for the suddenly centered star. Roberts felt so comfortable on the set that she literally took some of it home with her—buying her character’s bedroom furniture, assembled by decorator William Wright, for $25,000. The British colonial-style bed, lamps, tables and chairs—plus Indonesian shadow puppets and a ceramic pig—all wound up at her Taos home.

Not that she will be able to spend much time there, enjoying the new decor. Later this summer, Roberts (minus her curly tresses) will be out promoting the thriller Conspiracy Theory with Mel Gibson. That shoot also reflected the new Julia, degenerating at times into a practical joke-off: Gibson sent Roberts a gaily wrapped dead rat—and she responded by Saran-wrapping his dressing-room toilet. At that film’s wrap party in an L.A. nightclub on Feb. 8, Roberts got onstage and danced with abandon to the beat of the Funky Hippez.

And the future? Despite talks, a Pretty Woman sequel has never come to fruition, but a source close to Roberts says she may reteam with Richard Gere next spring for a suspenseful romance called Manhattan Ghost Story. That film would shoot after she costars with her close friend Susan Sarandon, for the first time, in an as-yet-untitled drama in which Sarandon’s character, who is dying, teaches her ex-husband’s new girlfriend (Roberts) how to raise her children. Roberts is also considering a comedy in development that would reteam her with Everett, who would play her gay husband.

Eventually, however, Roberts’s work may take her far from Hollywood. A friend says that every time Sally Struthers pleads for orphans on TV, “Julia gets a pen and writes down the address.” Everett predicts that Roberts, who spent six days touring Haiti in 1995 on behalf of a literacy project, will become a leader of UNICEF, following in the footsteps of the late Audrey Hepburn. “Just wait and see,” Everett says. “When she’s 50, she’ll have her shirtsleeves rolled up, and she’ll be scrubbing babies in Calcutta.” But in between movies, her fans hope. Says Pretty Woman director Garry Marshall: “She wants to be risky, be brave, not just make franchise movies. She’s very serious about acting. The critic who didn’t like Mary Reilly will be long gone, and Julia Roberts will still be working.”