Perhaps it should come as no surprise, but an HBO movie about one of the most politically charged periods in recent American history, when U.S. policy in Vietnam unraveled under the weight of lies and missteps, is causing a little fresh debate and rancor of its own.

"A Bright Shining Lie," based on the Pulitzer Prize-winning book by Neil Sheehan, who covered the war for United Press International and the New York Times, tells the story of U.S. involvement through the life of John Paul Vann, a hard-driven colonel turned civilian adviser who was among the first to blow the whistle on U.S. policy mistakes through such reporters as Sheehan and David Halberstam, who also met Vann while covering the war for The Times.As the book disclosed, Vann, who died in a helicopter crash in Vietnam in 1972, also had a hidden dark side, being haunted by his illegitimate birth and charges of sexual misconduct with an underage baby sitter.

Sheehan said that he appreciated the effort the filmmakers had made but that he was disappointed in the finished film. Two of the prominent characters in the story, Halberstam and Daniel Ellsberg, who worked with Vann in Vietnam, demanded that their names be removed from the characters in the film after reading an early draft of the screenplay by Terry George, who also directed the film.

Ellsberg was a member of the team that wrote the Pentagon Papers, a secret history of the U.S. involvement in the war. Neither Halberstam nor Ellsberg has seen the finished film yet, but some of what they had objected to is still present.

John Vann, an investment adviser in Dallas who is John Paul Vann's son and executor, was also upset with the early screenplay and is contemplating legal action on behalf of Vann's survivors. But he said he was waiting to see the final film before making his decision. He had been promised a videotape, but has not received it.

"The adaptation mixes a lot of complicated facts in an attempt to tell a complicated story," Vann said. "Very few people knew my father like Dan or Neil or Halberstam did. He was a very passionate, caring man who believed very much in doing the proper thing. The sizzle that's being put into it may sell movies but it certainly doesn't do much to explain the man or the war."

George says it was inevitable that such a complicated book would need to be pared down to fit into a two-hour time slot and that alterations of fact and composite characters were necessary to keep the story clear and to build dramatic interest. He acknowledged that "you're the ultimate target" when you try to do that.

"Of necessity, you're forced to compress and composite and put together composite scenes to tell a linked and cohesive story," he said. "What they saw was a very early script. I hope they feel differently when they see the finished film."

The movie is a serious attempt to do justice to an important book, George said, and any changes were made with an eye toward remaining faithful to the spirit of Vann and his story.

"In the script I was shown, it was a movie with zero historical interest," Ellsberg said. "The emphasis was on drama, and very cheap drama at that. That was not John Paul Vann in the movie."

Ellsberg objected particularly to three scenes involving Vann: one in which he bitterly confides to the Ellsberg character about his mother's past as a prostitute ("That conversation did not take place,and I do not believe that John expressed such sentiments to anyone"); one where Vann slaps a South Vietnamese officer in front of his troops ("an amazing action for which he would have been expelled from Vietnam immediately") and one where he reacts callously to the death of a Vietnamese schoolteacher ("That is the opposite of John as a person and as a political figure").

"Every scene is fictional, every line is fictional," Ellsberg said. "They had taken almost nothing from this 800-page book, which is filled with marvelous human incidents."

In the final film, Vann still expresses bitterness about his mother to the Ellsberg character, now named Doug Elders and a composite of Ellsberg and Douglas Ramsey, who also worked with Vann. The scene with Vann slapping the Vietnamese officer is retained, but the schoolteacher scene no longer has Vann reacting callously.

George was nominated for an Oscar for co-writing the script of "In the Name of the Father" (1993); he wrote and directed "Some Mother's Son" (1996) and wrote last year's "The Boxer." All concerned Northern Ireland.

He said he was aiming in the film not only to make a study of "this deeply flawed character" but to attempt to capture the entire sweep of the war, from its early gung-ho days to the final disillusionment, because he believed young people were unaware of what really happened during the war and how it changed the United States and the world.

The film, which will premiere Saturday on HBO, was shown three times recently - including at a gathering of Vietnam-era policy-makers and journalists at the Council on Foreign Relations.

Sheehan, who has seen the finished film, elected not to take part in those events. He said he sincerely appreciated the efforts that the filmmakers made and believed it was a serious attempt to translate the book onto the screen.

"I am sorry that they didn't succeed in pulling it off," he said. "It's not that Vann is portrayed in a derogatory way. It's that his character is not fully developed."

In attempting to tell Vann's story and the entire story of the war, the film became too diffuse.

"So you don't come out with a film that gives you a lot of insightful history, nor do you come out with a film that is a riveting character study of John Vann," Sheehan said. "It's not a bad film. It's just that they didn't succeed."

The judgments were much more upbeat at the screening at the Council on Foreign Relations.