ON CHRISTMAS Day, Twentieth Century Fox released the long-awaited movie, "Hoffa," starring Jack Nicholson as Jimmy Hoffa, the powerful Teamster leader. To complement the film, a "novelization" has been available for several weeks in the nonfiction section of America's bookstores, which is curious, since the publisher confesses on page 309 that "Although this story is based on fact, the acute reader will notice several departures from reality."

That remark should win a prize for the understatement of the year. And the movie certainly confirms it. Few reality-based motion pictures have blended fact and fiction as much as "Hoffa."

Like last year's Oliver Stone movie, "JFK," and other recent Hollywood portraits, the Danny DeVito/David Mamet epic is interesting drama but terrible history. In seeking to recast controversial characters as more sympathetic heroes, screenwriters are repackaging and slanting -- even fabricating -- real events to be more favorable toward their principal subjects.

When I called the film's executive producer, Joe Isgro, to ask why the movie of this complex man was so heavily fictionalized, he replied, "That's a David Mamet script; he wrote it entirely on his own." Mamet, a wonderful playwright, screenwriter and director, has never been known as a nonfiction writer. "Hoffa" demonstrates that he hasn't any interest in becoming one.

In "Hoffa," DeVito and Mamet use minor events in the Teamster leader's life to portray him as a champion of rank-and-file workers, omitting the harsher realities of his clear-cut corruption. Hoffa, played with panache by Nicholson, is shown as a man who dealt with mobsters at arm's distance and only when necessary. For instance, in one of many misrepresentations, DeVito/Mamet dramatize Hoffa's initial association with the Mafia as a means of organizing an oppressive employer who refused to be unionized. In fact, Hoffa's pact with the underworld came about in 1941, after a union local belonging to the Congress of Industrial Organizations (CIO) threatened the Teamsters' turf in Detroit. Hoffa sought out the mob's help to drive this union out of town. The CIO's defeat, brought about by Hoffa's ringers, became the major factor in his rapid descent from working-class hero to labor racketeer.

In the wake of this pact, the Mafia owned Jimmy Hoffa. When mobsters Jimmy Quasarano and Peter Vitale needed a facade of legitimacy for their Detroit-based narcotics operations, Hoffa created a dummy Teamsters local for them to run. When Hoffa discovered that his wife was having an affair with Tony Cimini, another Detroit mobster, Hoffa went hat-in-hand to Joe Zerilli, the boss of the Detroit Mafia, and begged him to order Cimini away from his wife. When the mob needed the means by which it could send a fleet of C-74 Globemaster aircraft to the new Cuban government in 1959 in a failed effort to protect its gambling and narcotics operations, Hoffa obliged and greased the process. When the underworld needed money to build its casinos in Las Vegas, Hoffa allowed it to use the Teamsters pension fund as a bankroll.

Ironically, one important character missing from the Hoffa story was also missing in "JFK": Carlos Marcello, the New Orleans Mafia boss. He was an associate both of Hoffa and of Jim Garrison, the district attorney in New Orleans who was deified in "JFK." Neither film included the fact that Garrison attempted to discredit Edward Partin, the key government witness against Hoffa in the Teamster boss's jury tampering trial in 1964. Hoffa was found guilty, largely on the strength of Partin's testimony, and was sentenced to eight years in prison.

Partin, who died in 1990, told me that during Hoffa's appeal process, Garrison (as a favor to either Hoffa or Marcello or both) investigated him as a suspect in his already off-the-wall New Orleans probe of the murder of President Kennedy. An attorney for Hoffa, Frank Ragano, says he approached Partin and told him that he could make Garrison go away -- if Partin agreed to sign an affidavit recanting his earlier testimony against Hoffa. Partin refused; Hoffa went to Lewisburg Penitentiary in March 1967 and remained there for more than four years.

Oliver Stone and DeVito/Mamet ignored this series of events. Instead, their respective screenplays enshrine Hoffa and Garrison as misunderstood visionaries who were toppled for unjustified reasons by unprincipled and ruthless adversaries using the full force of the United States government.

The omission is doubly ironic because of new evidence implicating Hoffa in the assassination of John Kennedy. Earlier this year, Frank Ragano offered to turn state's evidence regarding his knowledge of the roles of Hoffa and Marcello in Kennedy's murder. According to Ragano, Marcello and Santo Trafficante, the former Mafia boss of Tampa, accepted a murder contract on Kennedy from Hoffa in 1963. Ragano has told me that Garrison did nothing more during his 1967-1969 investigation than divert public attention away from Marcello. "Garrison was shielding Marcello from being implicated in the Kennedy murder case," Ragano says.

Both Stone and DeVito/Mamet had ample time to study these widely publicized findings. Despite the existing evidence of Garrison's collusion with Hoffa and Marcello, Stone chose to dismiss it. (He blamed several agencies of the federal government for the president's murder.) DeVito/Mamet also ignored Hoffa's plotting against Kennedy and chose instead to celebrate Hoffa's life.

In a movie where a real-life bad guy is made to look good, it is not surprising that a real-life good guy is made to look bad. Case in point: Robert F. Kennedy, who served in the 1950s as the chief counsel of the Senate Rackets Committee investigating Hoffa and later as U.S. attorney general. Predictably, the film depicts Robert Kennedy as obsessed, egomaniacal and power-hungry. However, the facts here are clear too. The Kennedy brothers waged a legitimate and effective war against Hoffa, the underworld, and their associates. Robert Kennedy proved to be the most effective organized crime fighter in this country's history.

Such manipulations are a favorite device of Mamet's. He also wrote the screenplay for the 1986 movie, "The Untouchables," which takes liberties with the life of its hero, Eliot Ness. He portrays Ness as committing an act of cold-blooded murder: Near the end of the movie Ness throws mobster Frank Nitti from the roof of a Chicago building to his death. In reality, Nitti committed suicide by shooting himself after being indicted for his role in a union shakedown scheme involving -- life imitates the art -- the Hollywood film industry.

But Mamet is not alone in purveying historical nonsense about mobbed-up union leaders. Earlier this year, HBO aired a made-for-TV movie, called "Teamster Boss," about Jackie Presser, another former Mafia-connected president of that union. In fictionalizing portions of this drama, HBO had the audacity to credit the corrupt Presser, who died in 1988 while under indictment for racketeering, with engineering the 1991 purge of the corrupt old guard in the Teamsters by the union's rank-and-file reformers.

The message from Hollywood and the publishing industry is clear: If there is inadequate evidence upon which to base a book or film with a controversial point of view, then fictionalize the story -- but promote the finished product as "reality-based" non-fiction. When mistakes and distortions are later alleged by critics or lawsuits are threatened, quickly remind everyone that the work is really only fiction "based on fact {with} several departures from reality." Hollywood producers and screenwriters must be amused, if not perplexed, by journalists and nonfiction writers who often risk life and limb in pursuit of true facts and have to face long, drawn-out libel suits if they're wrong. Meantime, fiction writers -- without leaving their word processors or the comfort of their homes -- can turn night into day, wrong into right, and make villains into heroes. And then, sadly, those fictionalized portrayals will do more to shape the public's perceptions of history than the most meticulously researched books and film documentaries. After all, it was the massive publicity over "JFK" that forced the federal bureaucracy to begin the process of releasing its sealed files about the president's murder. It was the right thing, but for the wrong reason.

Times have changed, even in Hollywood. The right things used to happen for the right reasons. In 1954, the Oscar for best picture went to "On the Waterfront," a fictionalized account of real events in which a Hoffa-like character, corrupt union boss Johnny Friendly (Lee J. Cobb), was done in by Terry Malloy (Marlon Brando), a fringe hoodlum who boldly defied union thugs and the mob by testifying against Friendly. Malloy's brave act paved the way for a free and democratic union. "On the Waterfront" served as the impetus for major federal, state and local investigations of corrupt unions and their partners in management. If "On the Waterfront" was remade today, Friendly would probably be repackaged as a persecuted working class hero, Malloy would become a cowardly stool pigeon, and the novelization would sell briskly in the nonfiction section of your local bookstore.

The updated version of Dan Moldea's 1978 book, "The Hoffa Wars: The Rise and Fall of Jimmy Hoffa," will be released in January.