Claude Lanzmann is in a bad mood. The director of “Shoah” is here to publicize the 25th anniversary re-release of that classic documentary and, whether he is jet-lagged or bored or subject to the cantankerousness that frequently befalls a man less than a week shy of his 85th birthday, he is in a bad mood and making no effort to conceal it.

Asked about the timing of the film’s re-release, which takes place on Dec. 10, he scowls and pronounces this “a foolish question.”

He barks, “This is not a film which has to be hidden. In France it is shown every two years on television and in the theaters, too. Why is it necessary to reread ‘War and Peace?’”

Lanzmann is just starting.

“It is the only great film about the Shoah,” he says. “It’s a very good thing that it is a young company [IFC] that is re-releasing it. They understand that the film showed people how distorted their view of the Shoah was. But after a while, the film fell into a sort of oblivion [here].”

Asked if there is anything he would change about the film, if the film has aged, he clearly considers these more foolish questions.

“No, no, no, no, it is exactly how the film is,” he says. “‘Shoah’ is like a source, like a wellspring. It creates its own necessity, its own actuality. It does not age. The film has not one wrinkle.”

For a moment a small smile plays around Lanzmann’s lips. He says of his subsequent shorter documentaries that were spun from the original interviews, “Some of them are not bad.” But then he adds, including just about every other film on the subject in his indictment, “‘Shoah’ is the only one that faced directly what has been, not trying to escape.”

Although the film’s nearly 10-hour running time consists almost entirely of the testimony of Jewish witnesses, Lanzmann bristles at the use of the word “survivors.”

“’Shoah’ is not a film about survivors,” he asserts. “It is a film about the radicality of death inside the gas chambers. I interviewed members of the Sonderkommando, witnesses to the last stage of the extermination process. Mr. Spielberg is dealing only with the feeble memories of ‘survivors,’” a reference to Steven Spielberg’s “Schindler’s List.”

And when the last of the witnesses is dead?

“Nothing will be forgotten,” he says. “You have no survivors of the First World War but everybody knows what happened, right? This obsession with ‘after the survivors’ is a stupid Jewish idea. ‘Shoah’ will remain as an absolute barrier against forgetting.”

His voice suddenly turns plaintive, quieter.

“I tell you this because I think it is the truth,” he says. “There is no vanity, no megalomania. But I’m tired of hearing this saying, ‘when the last survivor…’ It is not serious.”

There are times in “Shoah” when one feels that Claude Lanzmann is speaking a different language than any other filmmaker, perhaps different from any other Jew. The film’s influence on other documentarians has been enormous; it presents a unique (and uniquely just) solution to the problem of making a film about something that is absent, a film about a void that was once inhabited by six million human beings. Subsequent films have taken some cues from “Shoah,” yet there isn’t another film like it.

At one point in our interview, Lanzmann said that the people he interviewed for the film, most of whom had experienced the blackest reality of the extermination camps, call themselves not survivors, but “spokesmen of the dead,” doomed men whose witness came virtually from beyond the grave. Such a discourse would, of necessity, have a different import from what we are used to seeing and hearing in a movie. Perhaps that accounts in part for the singularity of the film.

But there is more. The sheer length of “Shoah” sets it apart from any other film on the subject. Even Marcel Ophuls, Lanzmann’s good friend (who also says that “Shoah” is “the greatest film about the Holocaust”), has only made four-hour-plus films.

I do not make the comparison humorously. Lanzmann sets a task for the viewer. There is no way to mistake “Shoah” for an evening’s casual entertainment, for a Hollywood-sanitized version of mass murder. The film’s rigorous structure, its exclusive use of contemporary (1980s) footage, its refusal to draw on the archives for the easy reactions created by familiar images, its sheer dogged insistence on the primacy of testimony — all these taken together place “Shoah” outside the normal film experience, much as the events the film recounts are an unprecedented and still unequalled singularity in human history. In comparison, even the most stern and sober-minded fictional treatment of this material seems contemptibly frivolous, and most other documentaries, even the very good ones, look half-hearted.

One can argue with Lanzmann about the future of Holocaust denial in the remainder of this century, but he is neither vain nor megalomaniacal when he argues for his film’s unique status. “Shoah” is not the only film about the murder of six million Jews, but it probably is the only utterly indispensable film about it.

Claude Lanzmann’s “Shoah” will have its 25th anniversary re-release on Dec. 10 at the Lincoln Plaza Cinemas (62nd St. and Broadway), with Part One being shown the first week and Part Two the second. The film will open at the IFC Center (323 Sixth Avenue) on Dec. 24.