Ivan Reitman, ‘Kindergarten Cop’s’ Top Sergeant : Movies: The director of ‘Ghostbusters’ and ‘Twins’ faces his biggest challenge yet: a room full of tykes. Even Arnold Schwarzenegger was cowed.

In order to preserve his sanity while working with 30 young children on “Kindergarten Cop,” director Ivan Reitman had to develop rather innovative methods of moviemaking.

“After the first day of filming I was in a sweat,” Reitman recalled last week in an interview in his lush office at Universal. “My shirt was all wet, my voice was hoarse and I had this really panicked look in my eyes. So I developed the five Reitman rules of filmmaking--listen, act natural, know your character, don’t look in the camera and discipline.”

Reitman admitted that he had no idea how hard it would be to work with a group of children between the ages of 4 and 7. “I had worked with 12- and 13-year-olds in ‘Meatballs’ and it worked out fine,” he said. “I thought, ‘I can handle this.’ ”

But he couldn’t.

“I suddenly realized how little they were,” Reitman said. “It was really tough.”

“Kindergarten Cop” stars Arnold Schwarzenegger as a tough police detective forced to go undercover as a kindergarten teacher who ends up falling for his young charges. The movie reteams Reitman and Schwarzenegger for the first time since their 1988 box-office hit, “Twins.” Reitman’s seven previous films--including “Meatballs,” “Stripes” and the two “Ghostbusters”--have grossed $3 billion worldwide, making him the most successful comedy director in history.

The majority of the children featured in “Kindergarten Cop” are non-actors from Southern California. Reitman and casting director Michael Chinich auditioned more than 2,000 children.

“We rented a school nearby and took over a couple of kindergarten classes,” Reitman said. “We would bring in about 150 kids at a time and we would see them in four sets of 35 at a time. They would stand up and introduce themselves and say anything they wanted to say.”

Each group was videotaped and photographed. Eventually, they narrowed the 2,000 down to 250 children. Reitman spent days trying lines with the 250 kids. “You would say, ‘Jason, start over there, walk to the exit while you are walking, say this line and after you say this line, go over there and pick up the basketball.’ ”

Reitman laughed. “You tell that to an adult and he may have some trouble with it,” he said. “If he’s an experienced actor he can usually handle it, but say that to a 5-year-old and all he can remember is basketball . By the time you finish talking and you say ‘action,’ he runs over and picks up the basketball and you have to start all over again.”

Schwarzenegger was brought in late during the audition process so he could get accustomed to talking with the youngsters. Though a new father, said Reitman, Schwarzenegger never had conversations with such small children.

“Most people don’t have to,” Reitman explained. “I have three kids, so I have learned to talk to kids a little bit. I don’t condescend to them. So he watched to see how I spoke to the class at first and then he started to pick up the fact I dealt with them as if they were young adults.”

“I think that everyone always tells you never to work with children or animals,” said Schwarzenegger. “But Ivan felt comfortable with the children. He is a family man himself and has taken his kids to kindergarten. By the time I got into the play, I felt he was in control of the children and knew exactly how to deal with them.”

Schwarzenegger admitted he was worried about how he was going to relate to the kids. “You read the script and it’s a great idea and then all of a sudden the dust settles,” he said. “That’s why I insisted Ivan direct the film. When I went in, I was sweating. I felt like the character in the movie. Then it dawned on me that physical fitness would be a way to approach them. I asked them to do jumping jacks and 100 kids enthusiastically started to do jumping jacks. We started exercising and from that point on, I had them totally on my side.”

“I think they softened his heart,” said Reitman. “He really got into the film.”

The 30 children ultimately chosen “made an interesting box together of assorted kids. It was mixing and matching. I wanted people coming out of the film to feel that this is a real kindergarten class, not just film kids.”

Identical twins Joseph and Christian Cousins play the leading child role of Dominic. “That was just luck,” Reitman said. “It was hard enough to find anyone who could approach those lines and in comes this kid--actually two kids walk in, and they were spectacular. I thought, ‘Thank God, not only is he good, there’s two of them!’ ”

The first phase of shooting in Oregon went smoothy because there were no complicated classroom scenes, Reitman said, but things changed quickly when they got to the sound stage at Universal.

“As soon as they got on the set it was pandemonium,” he said. “For some reason, as soon as the children see a camera they are like a magnet toward those beautiful eyes. The Pledge of Allegiance scene was not a hard scene, but because it was a close dolly shot of a long line of the kids, you could just see the kids go toward the camera as it went by.”

So Reitman would do tricks to get the kids’ attention. “I would walk beside the camera waving something so they would be distracted, or I was constantly talking while the filming was going on, reminding them what their lines were. I became a kind of cheerleader.”

Though several of the children could read, most were taught their lines by their parents. A lot of their dialogue, though, was written by Reitman the day of the shooting. The scene in which Schwarzenegger asks the students to explain what their fathers do for a living, was just a few lines in the script. “I gave some kids lines to say, but half of them were real,” he said. “They talked about what their real fathers did and they enjoyed that.”

Reitman’s favorite was 5-year-old Sarah Rose Karr, who plays Emma, a little girl who always needs to use the bathroom. “She marched to her own drummer,” Reitman said with affection. “I quickly learned not to worry about it. If she wants to stand, let her stand. If she wants to sit, let her sit. The class would be looking one way and she would be whirling about. She was just very special.”

Though the majority of the parents had never thought of their children as actors, Reitman said many showed symptoms of becoming stage parents by the end of production.

“They could see if little Sally was in the camera or not,” he said. “When they found she wasn’t, they would say, ‘Sally, maybe if you stood a little closer to Arnold. . . .”