Deep inside the forbidden zone at the U.S.-occupied Bagram air base in Afghanistan, around the corner from the detention center and beyond the segregated clandestine military units, sits a cluster of metal shipping containers protected by a triple layer of concertina wire. The containers hold the most valuable prizes in the war on terrorism -- captured al Qaeda operatives and Taliban commanders.

Those who refuse to cooperate inside this secret CIA interrogation center are sometimes kept standing or kneeling for hours, in black hoods or spray-painted goggles, according to intelligence specialists familiar with CIA interrogation methods. At times they are held in awkward, painful positions and deprived of sleep with a 24-hour bombardment of lights -- subject to what are known as "stress and duress" techniques.

Those who cooperate are rewarded with creature comforts, interrogators whose methods include feigned friendship, respect, cultural sensitivity and, in some cases, money. Some who do not cooperate are turned over -- "rendered," in official parlance -- to foreign intelligence services whose practice of torture has been documented by the U.S. government and human rights organizations.

In the multifaceted global war on terrorism waged by the Bush administration, one of the most opaque -- yet vital -- fronts is the detention and interrogation of terrorism suspects. U.S. officials have said little publicly about the captives' names, numbers or whereabouts, and virtually nothing about interrogation methods. But interviews with several former intelligence officials and 10 current U.S. national security officials -- including several people who witnessed the handling of prisoners -- provide insight into how the U.S. government is prosecuting this part of the war.

The picture that emerges is of a brass-knuckled quest for information, often in concert with allies of dubious human rights reputation, in which the traditional lines between right and wrong, legal and inhumane, are evolving and blurred.

While the U.S. government publicly denounces the use of torture, each of the current national security officials interviewed for this article defended the use of violence against captives as just and necessary. They expressed confidence that the American public would back their view. The CIA, which has primary responsibility for interrogations, declined to comment.

"If you don't violate someone's human rights some of the time, you probably aren't doing your job," said one official who has supervised the capture and transfer of accused terrorists. "I don't think we want to be promoting a view of zero tolerance on this. That was the whole problem for a long time with the CIA.."

The off-limits patch of ground at Bagram is one of a number of secret detention centers overseas where U.S. due process does not apply, according to several U.S. and European national security officials, where the CIA undertakes or manages the interrogation of suspected terrorists. Another is Diego Garcia, a somewhat horseshoe-shaped island in the Indian Ocean that the United States leases from Britain.

U.S. officials oversee most of the interrogations, especially those of the most senior captives. In some cases, highly trained CIA officers question captives through interpreters. In others, the intelligence agency undertakes a "false flag" operation using fake decor and disguises meant to deceive a captive into thinking he is imprisoned in a country with a reputation for brutality, when, in reality, he is still in CIA hands. Sometimes, female officers conduct interrogations, a psychologically jarring experience for men reared in a conservative Muslim culture where women are never in control.

In other cases, usually involving lower-level captives, the CIA hands them to foreign intelligence services -- notably those of Jordan, Egypt and Morocco -- with a list of questions the agency wants answered. These "extraordinary renditions" are done without resort to legal process and usually involve countries with security services known for using brutal means.

According to U.S. officials, nearly 3,000 suspected al Qaeda members and their supporters have been detained worldwide since Sept. 11, 2001. About 625 are at the U.S. military's confinement facility at Guantanamo Bay, Cuba. Some officials estimated that fewer than 100 captives have been rendered to third countries. Thousands have been arrested and held with U.S. assistance in countries known for brutal treatment of prisoners, the officials said.

At a Sept. 26 joint hearing of the House and Senate intelligence committees, Cofer Black, then head of the CIA Counterterrorist Center, spoke cryptically about the agency's new forms of "operational flexibility" in dealing with suspected terrorists. "This is a very highly classified area, but I have to say that all you need to know: There was a before 9/11, and there was an after 9/11," Black said. "After 9/11 the gloves come off."