"Ordinary People," the somber story of an American family torn apart by the death of a son, was chosen Best Picture of the Year last night at a none-too-jolly 53rd annual Academy Awards ceremony in Hollywood.

Sissy Spacek was named Best Actress for playing country singer Loretta Lynn in "Coal Miner's Daughter," Robert De Niro Best Actor for playing ultra-pugnacious boxer Jake LaMotta in "Raging Bull," and Robert Redford got the Best Director Oscar on his first effort as a director, "Ordinary People."

For only the third time in Oscar history, the ceremony was postponed from its original day (Monday) because of extraordinary circumstances: the attempted assassination of President Ronald Reagan. Host Johnny Carson told the audience last night that "it would have been inappropriate to stage a celebration" on such a dark day.

A taped message of greeting, recorded a week ago in the White House by President Reagan, was shown to the crowd and the world-wide television audience at the start of the proceedings. On the tape, Reagan looked fit and chipper, and the former card-carrying member of the Motion Picture Acedemy joked of the Oscar-cast's theme -- "Film is Forever" -- that "I've been trapped in some film forever myself."

Carson said Reagan had asked for a TV set in the hospital room where he is recovering from a gunshot wound so that he could watch the ceremony, but it didn't seem likely the president would tax his strength by staying up through the entire, arduous, three-hour show.

"Ordinary People," which had been nominated for six awards, won four: Best Picture, Best Director, Best Supporting Actor and, to Alvin Sargent, Best Screenplay adapted from another medium.

The only other films wining major multiple awards were Roman Polanski's "Tess," which was citied for costume design, art direction and cinematography, and Martin Scorsese's "Raging Bull," which won, in addition to De Niro's Oscar (the second of his career) the award for the Best Editing.

But to some degree everything seemed an anticlimax to the Reagan opening, and the tragic events in Washington a day earlier did put a shadow of gloom over an affair that had promised to be grim enough anyway -- since all but one of the year's Best Picture nominees were somber, austere films, and nothing to shout about.

References to the shooting, or at least to violence in America, kept cropping up in acceptance speeches. Writer Sargent noted proudly that his screenplay contained "no bullets and no guns and no rapes and no homicides." In his rambling speech, De Niro made reference to "all the terrible things that are happening" in the world.

While De Niro made his remarks, cameras cut to a shot of the man he portrayed in the film, hot-headed boxer Jake LaMotta, who was sitting in the audience. De Niro did the bynow traditional marathon of thanks ("I want to thank my mother and father for having me and my grandmother and grandfather for having them"), also thanking LaMotta's brother Joey, "even though he's suing us."

Spacek, honored for her portrayal of Loretta Lynn, told the audience, "This is the greatest! For the first time in my life, I'm speechless." She held the statuette with both hands and her last words from the podium were, "and Mom and Daddy, I love you too."

As with all Oscar telecasts, there were the usual outlandish getups (Mary Tyler Moore's dress had an air-bag sleeve), chronic embarrassments (Peter O'Toole and Dustin Hoffman were lengthier in thier presentations than most winners were in their acceptances) and bona fide sentimental heartwarmers, as when Lillian Gish, 81, stepped forth to present the Best Picture Oscar.

On a night keyed to movie nostalgia and the glories of the past -- glories of the present being, perhaps, in short supply -- veteran directors George Cukor and King Vidor made a welcome twosome when they presented the Best Director award and Vidor thoughtfully pointed to the cue cards so Cukor would read his lines.

Although he recently won the Director's Guild award for "Ordinary People" and was widely predicted to win last night, Redford told the throng, "Well, I didn't think I was going to see this" upon winning. He expressed "the greatest gratitude" for the "trust" he got "from a terrific cast . . . I love them and I appreciate their love, too."

Hutton played the profoundly troubled son in "Ordinary People." He thanked Redford ("I love ya," he said to the actor, attending his first Oscar-cast and seated in the audience) and also "my father," actor Jim Hutton, who died in June of 1979. "I wish he was here," Hutton said.

Steenburgen played the put-upon and pixilated wife of Melvin Dummar in "Melvin and Howard"; a high point of her lovable performance was a tap dancing routine to the Rolling Stones' "I Can't Get No Satisfaction." Steenburgen thanked, among others, her "patron saint," actor Jack Nicholson, who she said cast her in her first big role, opposite him, in the flop comedy "Goin' South."

Clutching her Oscar, Steenburgen gushed, "Well, I'm gonna have to think of something new to dream about, that's for sure."

Among the emotional highlights of the program was a Special Oscar to Henry Fonda, who never won one in competition, for all his memorable screen performances through a 46-year film career." "I feel I'm a very very lucky man," Fonda said. He walked onstage using a cane.

"It's been a very rewarding 46 years for me, and this has got to be the climax," said Fonda, 75. "I'm very proud and very grateful to the governors of the Academy. Thank you very much."

Go Goldman won the Best Original Screenplay Oscar for "Melvin and Howard," the whimsical tale of how Melvin Dummar met Howard Hughes and was momentarily rescued from obscurity by seeming to be mentioned in the recluse millionaire's will. Goldman said "Movies are made on faith and the studio's money" and so thanked, among others, Universal executive Ned Tanen "for his deep pockets."

Categorical delights on the program were few, but they included an appearance by the venerable Nicholas Brothers, one of the great dance teams in the history of motion pictures. The brothers appeared live immediately following a clip of them doing splits down a giant staircase in the 1943 production "Stormy Weather."

The crowd also cheered rotund tenor Luciano Pavarotti, who sang "Come Back to Sorrento" in Italian after a series of excerpts for movie musicals. Pavarotti was then joined by Angie Dickinson -- who carried a rose to Pavarotti onstage and told him "You're wonderful" -- to present the Oscar for Best Original Song.

It went to "Fame" the title tune from the musical about ambitious youngsters trying to barge into the big time in New York. Composer Michael Gore, who cowrote the song, was also the surprise winner for Best Original Score for the film.

Also brightening up the proceedings, if only slightly, were the fluffs and goofs that have become a part of the ritual, starting with the announcer who identified the host as "John Carson" and including Pavarotti's charming error in saying that "On the Road Again" was written by "Willie Wilson" (instead of Willie Nelson). Richard Chamberlain, presenting an award, pronounced "Mao" as "Mo."

And a shot of director Martin Scorsese ("Raging Bull") in the audience was identified as actor Michael O'Keefe ("The Great Santini").

The year's highest grossing film, "The Empire Strikes Back," was nominated in only three categories. It won for best sound and was also given a special board of governors' award for outstanding achievement in special effects. In accepting that award from Motion Picture Association of America (MPAA) president Jack Valenti (mysteriously the butt of some cold Carson barbs), one of the winners acknowledged the contribution of "The Force."

The award for Best Foreign Language Film went to the Soviet-made "Moscow Does Not Believe in Tears." Judged best documentary feature was "From Mao to Mozart: Isaac Stern in China." Producer Murray Lerner made reference to the "senseless violence in the world" in his acceptance speech. Best documentary short was "Karl Hess: Toward Liberty," a chronicle of a former Barry Goldwater speechwriter.

Among the awards announced in advance and presented at the ceremony was a scientific award for the optical printer, a device that facilitates composite images of live actors and exotic or preposterous backgrounds. Scenes from "King Kong," "Close Encounters," "Altered States" and "Superman" were shown to illustrate the wonders of the gadget.

ABC-TV estimated before showtime that the broadcast would be seen in a record 65 foreign countries with a potential viewing audience of 168 million homes and 300 million people. The ceremony went live by satellite to Australia, Brazil, Canada, the Dominican Republic, Mexico, Puerto Rico and Venezuela -- as well as the United States -- from the Dorothy Chandler Pavilion in Los Angeles.