In the new Coen brothers comedy "The Ladykillers," Tom Hanks trades his California-bred baritone for an outsized drawl that reminded one movie reviewer of a cross between William Faulkner and Maj. Charles Winchester of "M*A*S*H."

But the person behind the hybrid accent has nothing to do with the small-town Mississippi world of Hanks's Goldthwait Higginson Dorr III. She is Liz Himelstein, a native of Fort Wayne, Ind., one of a handful of Hollywood dialect coaches used by Mr. Hanks and other top actors to refine and teach the accents demanded by period or regional movies.

In the past decade, Ms. Himelstein, a former professor of speech at Carnegie Mellon University, has coaxed a Maine accent out of Memphis-born Kathy Bates in "Dolores Claiborne," helped Naomi Watts stifle her Australian accent to play the all-American Betty Elms in "Mulholland Drive," and sculpted the North Dakotan inflections for the characters in "Fargo." More recently, Himelstein worked with Australian-raised Nicole Kidman to hone an upper-class East Coast accent for the Lars von Trier film, "Dogville," also out this week.

At a recent voice session in her home, Himelstein led Brazilian-born Anna Carolina Dias in a workout that combined elements of yoga, primal scream therapy, and baby talk.

Dias, a youthful brunette with a wide smile and eager-to-please attitude, moved to New York as an adolescent. She wants to replace her voice - a combination of Portuguese-accented English and New York street cadence - with a neutral American one favored by casting directors.

After the two women warm up with stretches, deep breathing, and a couple of belly-rattling body shakes, Himelstein walks Dias through vocal exercises:

"MY MY MY MY."

"Budaka budaka budaka."

"Lippity lippity lop."

"WEE WAW WEE WAW WEE WAW."

For "Ladykillers," the Coens wanted their lead character's voice to combine an articulate Northeast accent with a Missisippi drawl, Ms. Himelstein says. Using poetry, monologues, and phonetic breakdowns, she drilled Hanks an average of two hours a day on the set.

"One of the sounds he uses is called a liquid 'u' - as in TYUES-day and STYU-dent - so we practiced that over and over again," she explains. For homework, she had Hanks repeat phrases: "The stupid student from Stewart's Institute sang the duke's new tune on Tuesday at the studio."

Not long ago, marquee actors avoided accents as today's starlets avoid carbohydrates, in part because they didn't want to risk tampering with their public personas. Consider the 1940 Ernst Lubitsch comedy, "The Shop Around the Corner." The film was set in Budapest, yet the stars, Jimmy Stewart and Margaret Sullavan, spoke with no trace of a Hungarian accent.

Today's audiences expect more from actors, who increasingly hail from all corners of the world. "It's a very demonstrable way of showing your acting chops, if you can pull it off," says Paul Dergarabedian, president of Exhibitor Relations Co., a box-office tracking and analysis firm in Los Angeles.

Indeed, accents have impressed Academy Awards voters in recent years. Tim Robbins and Sean Penn each picked up Oscars last month for their R-dropping roles as South Boston natives in "Mystic River." Last year, New Yorker Adrien Brody won the best actor Oscar for playing a Polish Holocaust survivor in "The Pianist."

At the same time, taking on an accent can work against an established actor. "If you do a bad job or the accent comes and goes, it can really change what could have been a good performance into a total disaster," Mr. Dergarabedian says. Critics slammed Harrison Ford, for instance, for feigning a Russian accent in the submarine drama "K-19: The Widowmaker."

Like many behind-the-scenes players, Himelstein is most proud of work that isn't noticed by the average moviegoer. "My best review would be that no one ever mentioned me or the accent," she said. "The only movie where it was imperative, when the accent was another character, was 'Fargo.' "

To coach Frances McDormand and other cast members on the dialect used in the 1996 black comedy, Himelstein gathered tapes of people speaking from all over North Dakota. She also took the actors on field trips.

"We were living in a hotel that was attached to a mall and we would go and have coffee or lunch and listen to the sounds around us," she said. "We couldn't believe people really did speak that way."

Besides Kidman, Himelstein's speech clients include Helen Mirren, Charlize Theron, and a handful of aspiring actors looking to erase all audible traces of Brooklyn, Sydney, or wherever they might have once called home.

Ms. Dias, for example, visits Himelstein once a week at her home. After her warm-up, they move on to whole phrases - "Betty bought a bit of butter" and "Sixty-six pretty women slipped into the city" - with Himelstein interjecting suggestions like "let's hear more 'zzzzz' there."

"What we're trying to do is get to the neutrality so that you have options," she told Dias. "Then you can do Shakespeare in the Park, you can go on the WB or CBS, you can do a film and be from Ohio if you need to be. You can be anything."

"Yas," Dias agrees, beaming at the prospect.

"Eh, eh...YEHS," her teacher corrects.