Sissy Spacek didn't know; Costa-Gavras didn't, either. Why was Universal Pictures putting on a big show in Washington for the opening of "Missing," filling the Uptown Theater with reporters, lawmakers and other types of Washington VIPs, and filling a smaller group of them later with roast lamb and wild rice at dinner?

Producer Edward Lewis had an idea. "We wanted to reach opinion makers," he said. "I would have preferred a series of small screenings like we had in L.A., but the people here told me that the only way you can get opinion makers here is to have a big do like this."

None of them thought it the least bit odd that the film everyone had been invited to see was the story of a young American who is summarily interrogated and tortured in Chile, with, the film implies, the knowledge if not the concurrence of officials in the American Embassy. Official Washington is portrayed as callous, capable only of bureaucratic double-talk and ineffectual protestations to a devious set of diplomatic and military advisers who all but engineered a military coup that claimed thousands of lives through torture and execution.

Guaranteed to provoke a few opinions among the opinion makers.

"It clearly has an ideological direction and should not be taken as anything more than the director's view of reality," said Jerrold Schecter, former senior diplomatic correspondent for Time magazine, ex-spokesman for Carter administration security adviser Zbigniew Brzezinski, and now working for Occidental Petroleum. Did he enjoy the movie? "Not particularly."

"There is no message, just a personal story," said director Costa-Gavras. "I never thought all the official people were villains. . . . But it is factually true that they knew the boy was dead when they told the father he was missing, that they sent the body back seven months later. . . . If there is a message, it is a message for the victims of President Augusto Pinochet."

While members of the current administration had been invited, few accepted and fewer came. Meanwhile "ex's and formers," as Alfred Friendly Jr., another former spokesman for Brzezinski, put it, such as former senators George McGovern and Frank Church, were much in evidence. The old dividing line -- whether you believe that American officials are capable of collusion with foreign madmen who shoot innocent people at whim -- seemed revitalized.

"I think it hits pretty close to home, and it happens other places, too," said Church, who was head of the Foreign Relations Committee that investigated the American role in the Chilean coup.

"It's completely false," said Cord Meyer, former CIA official. "I find it incredible that we sit here celebrating a movie that implies American diplomats agreed to this young man's death."

"I think it is a very important document. For me it was like a trip through the past," said Isabel Letelier, the wife of Orlando Letelier, the former Chilean diplomat who was killed when a bomb blew up his car here on Embassy Row.

Charles Horman's father, Edmund Horman, a retired businessman, came down from New York. The movie is really about the ordeal he and his daughter-in-law went through trying to find out what happened to his son. Horman was a conservative, Christian Scientist businessman, somewhat estranged from his more free-thinking only son. "Let me say this," he said, "I used to be naive."

He is played in the film by Jack Lemmon, who he thought was wonderful. Lemmon couldn't make it to the party; he was playing in a Pro-Am golf tournament in California.

Letelier, like Horman, thought the movie had significance beyond Costa-Gavras' declaration of simple artistic interest. "I saw a person shot right in front of me," she said. "That colonel in the national stadium (where thousands were detained) is someone I had to go and talk to for a year about people who were missing. . . . At this moment they are torturing people in Chile. In Congress they are trying to restore military aid to Chile. This movie could have a big impact on those who were present."