Like one of the characters in "Twilight Zone--The Movie," thrown by happenstance into the strange and unexpected, director John Landis was arraigned for involuntary manslaughter today just as the film that led to the charges opened in theaters nationwide.

In a loud, firm voice, the 32-year-old Landis, made wealthy and famous by films such as "National Lampoon's Animal House" and "An American Werewolf in London," pleaded "not guilty" to causing the deaths of his friend, actor Vic Morrow, and two child actors while filming a war scene last summer.

Los Angeles District Attorney Robert H. Philibosian said it was the first time he knew of that a film director had been criminally prosecuted for deaths or injuries occurring on a movie set. Superior Court Judge Ronald M. George released Landis and four other men charged in the accident on their own recognizance, as a mob of reporters and cameramen pushed and shoved for positions outside the courtroom.

Morrow, 53, and child actors Renee Chen, 6, and Myca Dinh Le, 7, died July 23 when debris from a special-effects explosion struck the tail rotor of a low-flying helicopter and caused it to crash on top of them. The actors were wading across a stream in a mock Vietnam war scene.

The slim, bearded Landis, dressed in a dark suit, read a short statement in a shaky voice after the brief court hearing: "The accident was an overwhelming tragedy for many people. It had a profound impact on our lives and I know in my head and I know in my heart that we did not cause this accident."

More than $80,000 in fines have been levied against Landis, Warner Bros., associate producer George Folsey Jr. and production manager Dan Allingham by the California labor commissioner's office and the state division of occupational safety and health in connection with the incident. The families of the three victims have filed wrongful death suits asking unspecified money damages against Warner Bros., Landis, Folsey and Allingham, plus Steven Spielberg, who coproduced the movie with Landis and directed one of its segments.

The court today unsealed grand jury indictments showing Landis had been charged with five separate counts of involuntary manslaughter, two for allowing the children on a desert filming location near Newhall, Calif., without proper permits and three for allowing the filming to allegedly proceed recklessly. Folsey and Allingham shared in the two counts for letting the children on the set. Paul Stewart, head of special effects, and Dorcey Wingo, the helicopter pilot, shared with Landis the three counts related to reckless filming.

Witnesses testifying before the National Transportation Safety Board said they heard Landis shout "lower, lower," in directing Wingo's flying of the helicopter. Landis has said the altitude of the aircraft was left up to Wingo. He also said the explosive charge that apparently caused the accident was "greater than expected."

One of the wrongful death suits filed against Landis and other members of the film crew refers to allegations in some of the safety board interviews that drugs and alcohol were consumed on the set and contributed to the cause of the crash. Asked about these charges at a news conference after today's court hearing, Philibosian said they were not part of the prosecutor's case against the five men.

Film industry executives have called Landis an unusually strong and well-organized director whose creativity and firm control over his projects have vaulted him at a relatively young age into the top ranks of filmmakers here. Critics generally have judged his segment in the Twilight Zone movie to be the weakest of the four, which also include efforts by directors Joe Dante and George Miller based on the long-running television series "The Twilight Zone."

Landis has received generally good reviews, however, for another recent release, "Trading Places," a modern version of the Mark Twain classic "The Prince and the Pauper" starring Dan Aykroyd and Eddie Murphy. Landis studied at UCLA and worked in the mail room at 20th Century-Fox studios before directing two low-budget movies, "Schlock," and "Kentucky Fried Movie." Their unexpected successes led to his directing "Animal House," which grossed more than $100 million.