Documentary about Shin Bet. Directed by Dror Moreh. (PG-13. 97 minutes.)

"The Gatekeepers," an Oscar nominee for best documentary, focuses on a handful of very tough guys. Israelis, generally speaking, tend to be tough, but the men who've commanded Shin Bet, Israel's secret service, are in a whole other category. They are in the protection business, but also in the pre-emptive killing business. They've seen things that curdle the blood, and they've done things that wake them up in the middle of the night.

Director Dror Moreh tells the story of Israeli's internal security, starting roughly with Israel's acquisition of the occupied territories in 1967 through today. Mainly he concentrates on the last 30 years and on the administrations of six Shin Bet leaders, who are very different in style and temperament, but who are all shrewd and pragmatic, with nothing of the ideologue apparent in their demeanor.

Most of us will never order a missile strike on a terrorist target, and so it's interesting to hear former Shin Bet head Yuval Diskin explain what it's like having to decide whether to fire in a matter of seconds, while assessing intelligence to find out whether innocent people are in the area. He says that sometimes the hardest thing is doing nothing, but that even the most surgical strike brings on a sense of dislocation. Even to him, it doesn't feel right that this power of life and death should be in his hands.

"The Gatekeepers" shows the aftermath of a suicide bomber's blowing up a bus, and it's one of the most eerie and disturbing sights imaginable. It's not disturbing in the sense of blood and gore but rather in the Hieronymus Bosch-like contortions of the bodies and in the ways it looks as if flesh and machine have fused, as though the people have gone to sleep and become part of the bus. It's unnatural, the modern obscenity of terrorism made visual and, in the most diabolical way, sculptural.

Now, having seen such a sight, imagine if it were your life's work to prevent that from ever happening again. Such a charge, and such life-and-death stakes, might easily make a person callous.

Avraham Shalom is an old man in red suspenders, who looks like a witty and whimsical grandfather. Then you find out that he ran Shin Bet between 1980 and 1986, and you notice the coldness and cunning in his eyes. Talking about an incident in which he ordered the summary execution of two Palestinians who'd hijacked a bus, he says, "I didn't want any more live terrorists in court." Ultimately, he had to resign over the incident.

All the men like "nice and tidy" operations, such as the one described as "elegant" by Carmi Gillon, who headed Shin Bet in the mid-1990s: A terrorist was executed using a cell phone bomb that blew up in his ear but caused no harm to anyone else. If you're running Shin Bet, that's as good as it gets. And the worst? The worst day in Shin Bet history came in November 1995, when Prime Minister Yitzhak Rabin was assassinated by a right-wing fanatic.

Rabin's murder came as a shock to Americans, but the film shows the extent to which violence toward Rabin might easily have been anticipated. The right-wing rallies, tacitly endorsed by conservative politicians, had become violent in their rhetoric, and Gillon had asked Rabin to wear a bulletproof vest. Rabin refused.

The documentary presents the death of Rabin, who was pursuing a lasting peace with the Palestinians, as a calamity for Israel, and the Shin Bet leaders share that assessment. It comes as a surprise: However they might have started out, they're all liberals now. Hardened, realistic, unsentimental and gimlet-eyed, but liberal - and that goes for Shalom, too, who favors negotiating with terrorists. Their positions on the big questions facing Israel - the settlements, the two-state solution, direct engagement with Hezbollah and other groups - place them decidedly to the left in the Israeli political spectrum.

Until this film, these Shin Bet directors had never consented to an interview. Now that they've spoken - and have said the unexpected - we can only wonder if their words will have an influence.