WHEN JAKOB Heym (Robin Williams) is called before a Nazi police commandant in 1944 for breaking a curfew, he overhears something that might just change everything.

In "Jakob the Liar," Jakob is the resident of an unspecified Jewish ghetto in Poland run by the Germans, where the trains come regularly to transport Jews to extermination camps. When he's caught by an overzealous Nazi sentry for being in the wrong place after 8 at night, Jakob expects death. The fact that it's not yet eight o'clock has no bearing on the subject.

As Jakob stands before the commandant, a radio broadcast suddenly comes on. The Soviet army has made gains against the Germans in Bezanika, a Polish town not too far from the ghetto. Could freedom be at hand?

Through a small comedy of errors, Jakob escapes being dispatched to the trains. He returns home, relieved to be alive and carrying this military information as if it were a secret, glowing ember of coal. Radios are forbidden in the ghetto. News like this -- in a place where death comes every day -- will rekindle hope.

The movie, based on a book by Jurek Becker and shot entirely on location in Eastern Europe, tells its story with admirable restraint. Director Peter Kassovitz, a 51-year-old Hungarian Jew, who saw both parents sent to the concentration camps (they survived), keeps a measured tone. But he's always aware that death and despair are very much in the air.

In the movie, Jakob's attempts to contain the information are impossible. A few whispers are enough to start rampant rumors. People even believe Jakob has his own radio and that he continues to monitor the progress of the war.

"I don't have a radio," Jakob tells Mischa (Liev Schrieber), an ex-boxer and ghetto resident.

"I understand," says Mischa, all but winking at him.

Like other residents, Mischa is filled with new hope. He decides to restart his training and to ask for the hand of his girlfriend Rosa (Nina Siemaszko). After all, as he tells Rosa's parents and just about anyone else who'll listen, the Russians are just a few hundred kilometers away.

Forced to feed the optimistic frenzy, Jakob tells people he does have a radio, and he even fabricates things he has picked up: snatches of jazz music, information about tanks made -- he claims -- in Chicago, and so on. The residents need it. The German trains keep coming for more victims.

There's another reason to keep the good news flowing. Jakob is harboring a young girl named Lina Kronstein (Hannah Taylor Gordon), who escaped from a transport train. When her health takes a turn for the worse, her only hope for survival is a strong spirit and good news from the front.

A Jewish doctor, Kirschbaum (Armin Mueller-Stahl), examines the girl. He can only prescribe boiled water and, as he tells Jakob, "some of your medicine, maybe."

In this movie, comedy and tragedy are tango partners, but it's unclear who has the lead. And if there's anyone to take us through such dark, uncertain terrain, it's Robin Williams.

Most of the time, the humor comes through ruefully. When Jakob visits his barber-friend Kowalski (Bob Balaban) for a free shave and a haircut, Kowalski is about to hang himself. But when Jakob makes his demand, he nonchalantly changes his mind and starts cutting. Incidentally, the town's staggering suicide rate, reports Dr. Kirschbaum, has suddenly dropped to zero.

All this thanks to someone who realizes he is setting the stage for freedom and potentially more death. Jakob has become the town's beacon of hope and, inevitably, its most endangered resident. But if telling lies can save a people, he reasons, let the stories -- and those fictional tanks -- roll.

JAKOB THE LIAR (PG-13, 120 minutes) -- Contains violence, sexual situations and emotionally harrowing material. Area theaters.