War was the name of the game last night at the Motion Picture Association of America. Well, almost.

Jack Valenti, MPAA president, had brought together about 70 guests from across the political spectrum to preview "Wargames," a $13.5 million movie about a teen-age computer whiz who starts with games and quickly learns how to "access" right into the Pentagon's master war machine, setting off a nuclear countdown.

While everybody agreed the film was good, fast-paced fantasy, some viewers could only take it seriously. Like Dr. Helen Caldicott of Physicians for Social Responsibility: "The planet is about to die. I think the government plays games like little boys . . . little boys playing with their missiles."

And like Sen. John Warner (R-Va.): "I'm anxious for people to learn, study . . . this movie may contribute to the people doing their homework. The key to this thing is self-education."

But Warner wasn't serious all evening. He found time to discuss his tennis game with talk show host Charlie Rose and Rep. Ed Markey (D-Mass.).

One person with a unique view on the movie, Defense Secretary Caspar Weinberger, declined to attend at the last moment, Valenti said. "He called up and said he was just too tired."

Was there a little calculated mischief involved with the guest list, such as including rivals on defense and nuclear freeze issues? "No," said Valenti, with just a hint of amusement in his eyes. "I think it gives it a kind of zest, an electricity.

"What people forget is that most of the professionals never take anything personally. In politics you never know if your enemy will be your friend. Most people outside of Washington don't understand that Republicans and Democrats are friends."

Among the guests were CIA Director William Casey, budget director David Stockman; Sen. Alan Cranston of California, who is a Democratic presidential candidate; Rep. Pat Schroeder (D-Colo.) and her son, Scott; Rep. Ron Dellums (D-Calif.) and his wife, Roscoe, and Roger Molander of Ground Zero.

Leonard Goldberg, who produced "Wargames," said the film's aim was to entertain, but it also had a message. The main character, David, "represents youth, optimistic youth," Goldberg said. "Despite his naivete he's more sophisticated than the adults."

How did he expect this Washington crowd to receive it? "It's a tough audience," he said, biting his lip during the dinner before the preview. "As Stockman just said, 'There's people here from the far right and people here from the far left. If you get an enthusiastic reception tonight, then the rest of America will be easy."

The rest of America is precisely what Molander, formerly a nuclear strategist, worries about. "It's clear that people want and need information about nuclear war."

Cranston, who called the movie "magnificent," added: "If nuclear war comes, it's apt to come by accident."

Rep. Ken Kramer (R-Colo.), who voted against the House nuclear freeze resolution Wednesday, thought the film had "an impact in terms of the potential consequences of the strategic arms race" and said he "agreed with the message but not the solution."

Stockman and Casey, apparently not eager to compare theater notes, hurried out as the movie ended.

In the film, a character named Falken, who helped devise the Pentagon war machine, says, "General, you are listening to a machine. Do the world a favor and don't act like one."

Markey seemed to echo that. "Not enough people in Congress understand how much we rely on computers and not on human beings to prevent nuclear war," he said. "Every senator should be strapped into a chair and made to watch this."