The growing threat of Germany's fascist hate groups is portrayed in the new TV film, The Infiltrator'.

A FORMER ISRAELI COP posing as an American neo-Nazi manages to infiltrate German fascist hate groups, where he uncovers new evidence proving they are bigger and more widely connected than had been thought.

It sounds like the plot of a Robert Ludlum novel, but this is the true story chronicled by Yaron Svoray in his 1994 book, "In Hitler's Shadow" (Doubleday). A gut-wrenching television movie adaptation of Svoray's story, retitled "The Infiltrator," premiered in North America on the HBO cable channel on June 24 and will be rescreened throughout July. Both the book and the docudrama recount the infiltration by Svoray, a former Israeli police detective, on behalf of the Simon Wiesenthal Center of Los Angeles, into neo-Nazi groups and hate organizations in the reunified German republic.

"The Infiltrator" stars Oliver Platt, a rotund young actor ("The Three Musketeers"), as Svoray; comedian Alan King as Wiesenthal Center director Rabbi Marvin Hier, and Peter Riegert ("Crossing Delancey") as Hier's skeptical and erudite deputy, Rabbi Abraham Cooper. It is directed with considerable craft by British filmmaker John MacKenzie ("The Long Good Friday").

Svoray first came across neo-Nazis in Germany in 1992, where he was posing as an Australian journalist researching a story about a cache of diamonds hidden in Germany by American soldiers at the end of the Second World War. Intrigued and disturbed by this new generation of fascists, he asked the Wiesenthal Center to back his attempt to infiltrate the far-right organizations.

Posing as an American neo-Nazi with access to funding, the beefy Israeli boozed and brawled with ultra-violent skinheads for several months, winning their confidence and using them to reach into the ranks of their ostensibly legitimate political backers in the rightist Republikan and NPD parties. Svoray turned up the first solid evidence that hate groups in Germany were much larger and better established than the Federal Republic had previously acknowledged; while German intelligence had asserted that the hate groups had fewer than 1,000 hard-core members, Svoray saw membership lists which put the rank-and-file at about 6,000. He also documented how these groups had used the Internet to circumvent German laws forbidding the import of fascist propaganda, and link up with Holocaust deniers and hate organizations in North America.

In May 1993 Svoray, Hier and Cooper presented their evidence to the Foreign Affairs Subcommittee on International Organizations and Human Rights of the U.S. House of Representatives. Responding to this unwelcome publicity, the Bonn government grudgingly asked them to appear before an ad hoc committee convened by the German Interior Ministry, which reacted apathetically to Svoray's findings.

Germany may have been glacial in acknowledging its neo-Nazi problem, but Hollywood saw a story in Svoray's mission. New York-based producer Francine LeFrak, winner of several Emmys for "Miss Rose White," a Hallmark Hall of Fame version of the Barbara Lebow play "A Shayna Meidel," heard from a journalist about Svoray's exploits, and met him in Los Angeles.

Astonished by the account, she set him up with an agent, called HBO, and told them to "clear the decks!" Svoray had a movie deal within a week. The cable company, reflecting the publicly stated interest of its president Michael Fuchs in Jewish subject matter, has produced a number of features in recent years dealing with the Holocaust, including "The Simon Wiesenthal Story" and "Fatherland" (a feature adaptation of the Richard Harris alternative history novel postulating a German victory in WWII). To commemorate Holocaust Memorial Day in May, it aired "One Survivor Remembers," a moving story of a Polish woman who survived a three-month death march into Czechoslovakia.

"To me," says LeFrak, "the most important thing was getting this word and story and message out as quickly as possible - and doing it with people who weren't going to tamper with it."

LEFRAK TOOK HER PRODUCTION to Hamburg, where she found

"a few left-wing neighborhoods" where she believed she could stage street brawls and sidewalk melees without inviting the real thing. The German and European press took immediate notice, much of it negative. So did the neighborhood, whose residents, many of them the same Turks who took the brunt of neo-Nazi rage in the film, were not pleased by the intrusion of skinhead brawls staged on their streets.

The screenplay by Robert Avrech and Guy Andrews takes some liberty with Svoray's narrative, mainly by streamlining it to combine some of the characters and episodes. That's relatively minor compared to the book itself, which Svoray co-wrote with Nick Taylor. The original manuscript of 750 pages was cut to 250 for publication. From the outset, LeFrak and MacKenzie realized that playing too fast and too loose with the facts would lose them credibility.

To assure this didn't happen, the filmmakers consulted with the Wiesenthal Center to ensure authenticity. Riegert spent a day with Cooper, and even wore one of the rabbi's yarmulkes in the film. But the movie's overly-reverential portrayal of Rabbi Marvin Hier would have been more authentic if Alan King had played him as Alan King, a Lower East Sider with a facile tongue and quick sense of humor, rather than the stereotyped rabbi in beard and fedora.

HBO is exploring the possibility of screening "The Infiltrator" in Germany and Israel either on television or in theaters. Meanwhile, LeFrak points to one small achievement. "I don't know what kind of effect it will have," she says. "But we had a mostly English crew (the interiors were all shot in London). The movie became personal to them, and they started looking around in their own neighborhoods. I think they felt they were working on something profound."