MOVIES : They Help Call the Shots : On the job: Sure, there are perks to being an assistant director, but the title can also mean 16-hour days, divided loyalties and lots of shushing.

As a veteran assistant director, Yudi Bennett thought she had been asked to do almost everything.

Then someone told her to find a pair of mice who could mate on cue.

For a brief scene in the 1988 comedy “A New Life,” Bennett asked university scientists to help stage a romantic encounter between two rodents. They ended up injecting the mice with hormones. The crew wrapped the delicate love scene as Bennett, who has served as assistant director on about 20 features, supervised wearing prop mouse ears.

Tough day at the office? Not really.

“It was easier than getting actors to do a lot of things,” she said.

Assistant directors seldom have it easy. Often hired by the director, they are responsible for a dizzying array of tasks, including scheduling the shoot, bringing actors to the set, staging background action and maintaining order during filming.

That’s the official job description. But in practice, assistant directors can be asked to do almost anything during production, and are answerable, in one way or another, to almost everyone: director, producer, cast and crew.

With more pictures falling into the hands of first-time directors with little or no film experience, the role of an experienced assistant director has become more important than ever in recent years.

“A cross between a cheerleader and a general” is how Bennett describes the job to puzzled relatives.

Stress and job-related injuries take their toll. Laryngitis is a common ailment. So are varicose veins and strained backs.

Why do assistant directors endure such aches and pains? Certainly not for the glory.

While such directors as Steven Spielberg or Quentin Tarantino have become household names, ADs (as they are known within the industry) toil in relative obscurity. Punishing 16-hour days on faraway locations can sometimes make them virtually unknown in their own households as well.

For many, the job serves as an entree to something else. A handful of famous directors started out as assistant directors, including Michelangelo Antonioni, Walter Hill and Alan Rudolph. Other ADs become unit production managers, producers or studio executives.

For others, the job is its own reward.

“It’s the little things” that make the job worthwhile, said Barry K. Thomas, puffing on a cigarette outside Stage 20 at 20th Century Fox, where he recently served as assistant director on the upcoming comedy “The Great White Hype.”

“I get to dress the way I want,” said Thomas, garbed in blue jeans and a dress shirt. “I like needing a map to get to work, always going someplace new. It’s a gypsy lifestyle.”

That gypsy aspect has not escaped the attention of filmmakers. Last year’s “Living in Oblivion,” about a director struggling to get his low-budget film shot, features an assistant director (played by Danielle von Zerneck) who breaks up with her cinematographer boyfriend--in between takes on the set.

Assistant directors have existed since the dawn of movie-making, though at first they were little more than glorified gofers. Their job functions increased with the advent of silent epics during World War I.

Joseph Henabery, who played Abraham Lincoln in D.W. Griffith’s controversial Civil War epic “The Birth of a Nation” (1915), served as one of the assistant directors on Griffith’s “Intolerance.”

Henabery told author Kevin Brownlow that he remembered spending much of his time researching costumes and other period detail. For the section of “Intolerance” set in ancient Babylonia, Henabery gathered a 15-foot-long shelf of history books, which he cut up and assembled into a scrapbook for easy reference. He also managed the “mob people”--thousands of extras, many of them shipped by trolley from skid row--and helped solve labor disputes. When a group of union hands refused to work overtime for the Crucifixion scene, Henabery grabbed a hammer and dashed to the gate of the lot.

“The first s.o.b. who tries to get out of this gate is going to get this hammer right in the head,” shouted Henabery, who went on to direct silent pictures starring Fatty Arbuckle and Rudolph Valentino.

Modern ADs wield power a bit more subtly. But their loyalties are sometimes divided among the director, production company and crew. In trying to help the director achieve his or her artistic vision, they can run afoul of the producer’s desire to keep costs down.

Jerry Ziesmer, an assistant director who worked on 50 films including “Apocalypse Now” before retiring in 1992, remembers occasionally wheeling and dealing with producers for special shots or equipment not in original budgets. If the production company would agree to spring for a crane, say, Ziesmer would agree to drop a few dozen extras.

The good assistant director “schmoozes the crew, schmoozes the cameramen--and finds the best way to realize the director’s vision,” Ziesmer said.

The Directors Guild of America, which includes 881 first assistant directors among its total membership of 10,000, tried to address the problem of split loyalty in 1981 by giving directors the power to hire their own assistants.

Yet the job itself remains as taxing as ever. In exchange for long hours and uninterrupted stress, an experienced assistant director can expect a decent paycheck (see accompanying story, Page 39) and a small credit at the end of the picture.

The sheer logistic challenges can be overwhelming. For footage of the runaway bus in the 1994 action hit “Speed,” assistant director David Sardi ordered a platoon of 65 production assistants to close down two square miles of Ocean Boulevard in Long Beach. For “Honeymoon in Vegas,” Bennett supervised a tricky three-night location shoot involving 25 skydivers dressed as Elvis Presley.

“We shot in the middle of the Strip, right outside Bally’s, and had 5,000 extras,” Bennett said. “One [parachutist] got hung up in a traffic light on Las Vegas Boulevard.”

Years of standing and shouting on various locations can take their toll.

On “Jaws,” Tom Joyner overcame problems with a malfunctioning mechanical shark and stubborn Martha’s Vineyard vacationers who refused to steer their yachts and sailboats out of camera range. But he wrenched his back by hoisting the anchor on the crew’s boat every day.

On subsequent films, “I had a little secret: I’d wear support stockings,” said Joyner, who produced the sequel “Grumpier Old Men” for Warner Bros. “It’s a tremendous help to your legs.”

No sure remedy exists for some of the headaches caused by colleagues, however. Many assistant directors have reported frustration with temperamental actors and novice directors.

Dustin Hoffman was to make his directorial debut with the 1978 drama “Straight Time.” But on the first day of shooting outside Folsom Prison, the actor could not decide where to put the camera for the first take, said Ziesmer, who served as assistant director.

“We must have moved the camera [without shooting film] 100 times that day,” he added. “He would ask the wardrobe person, ‘What do you think of this shot?’ ” The picture was eventually completed by director Ulu Grosbard.

Boredom is another potential foe.

Ziesmer was concerned because the late John Huston seemed distracted on the set of “Annie.” The AD tried everything he could think of to get the legendary director excited about the project. Then one day Huston asked Ziesmer to fetch a 27-inch TV monitor for the next day’s shooting.

“I thought, ‘Oh, boy, this is great! He really wants to see what’s going on [during shooting]!’ ” Ziesmer recalled. But his enthusiasm vanished when he learned the director requested the big monitor only so he could watch a broadcast of the Kentucky Derby.

Cast and crew are often tempted to banter between takes, which can delay filming and cost money. During shooting last summer on “Precious Find,” a science-fiction thriller starring Rutger Hauer, assistant director Martha “Marty” Elcan roamed the location--a defunct water treatment plant in Carson--repeating the same mantra:

“Here we go . . . very quiet . . . stay settled, folks . . . shhhhhhh . . . let’s roll please. . . . “

As Elcan, who once lost her voice supervising extras on a TV movie, told a visitor: “It sounds really imbecilic, but instead of going, ‘Quiet, everybody!’ I’m constantly going, ‘Shhhhhhh,’ so there’s this quiet layer all the time.”

But some assistant directors say the job takes the biggest toll after hours, at home. Many are often the first to arrive on the set in the morning and the last to leave at night. Unlike actors and directors, who are able to spend down time in air-conditioned trailers, ADs are in a state of continuous hustle.

“You’re away for 16 hours on the set and then you’ll come home and spend two hours on the phone before collapsing in exhaustion, and you don’t even have a conversation with anyone in your family,” said Sardi, who is married and has a 3-year-old daughter.

“You’re not aware of bankbooks and paying bills and home repairs--the day-to-day normal operation of a house, the things most people take for granted,” added Sardi, whose credits include “Nell,” “Waterworld” and “Nixon.” “You don’t want to feel like an absentee husband, an absentee father--but in reality that’s what you are.”

But at 39, he doesn’t plan to be an AD forever. Like so many others in Hollywood, he would like to direct his own picture some day--to call the shots instead of just scheduling them.

“AD-ing is a great career,” he said, “but it’s not an end-all and be-all.”