The system the CIA relies on to ensure that the suspected terrorists it transfers to other countries will not be tortured has been ineffective and virtually impossible to monitor, according to current and former intelligence officers and lawyers, as well as counterterrorism officials who have participated in or reviewed the practice.

To comply with anti-torture laws that bar sending people to countries where they are likely to be tortured, the CIA's office of general counsel requires a verbal assurance from each nation that detainees will be treated humanely, according to several recently retired CIA officials familiar with such transfers, known as renditions.

But the effectiveness of the assurances and the legality of the rendition practice are increasingly being questioned by rights groups and others, as freed detainees have alleged that they were mistreated by interrogators after the CIA secretly delivered them to countries with well-documented records of abuse.

President Bush weighed in on the matter for the first time yesterday, defending renditions as vital to the nation's defense.

In "the post-9/11 world, the United States must make sure we protect our people and our friends from attack," he said at a news conference. "And one way to do so is to arrest people and send them back to their country of origin with the promise that they won't be tortured. That's the promise we receive. This country does not believe in torture. We do believe in protecting ourselves." One CIA officer involved with renditions, however, called the assurances from other countries "a farce."

Another U.S. government official who visited several foreign prisons where suspects were rendered by the CIA after the attacks of Sept. 11, 2001, said: "It's beyond that. It's widely understood that interrogation practices that would be illegal in the U.S. are being used."

The CIA inspector general recently launched a review of the rendition system, and some members of Congress are demanding a thorough probe. Canada, Sweden, Germany and Italy have started investigations into the participation of their security services in CIA renditions.

The House voted 420 to 2 yesterday to prohibit the use of supplemental appropriations to support actions that contravene anti-torture statutes. The measure's co-author, Rep. Edward J. Markey (D-Mass.), singled out renditions, saying "diplomatic assurances not to torture are not credible, and the administration knows it."

Rendition, a form of covert action that is supposed to be shrouded in the deepest secrecy, was first authorized by President Ronald Reagan in 1986 and was used by the Clinton administration to transfer drug lords and terrorists to the United States or other countries for military or criminal trials.

After the 2001 attacks, Bush broadened the CIA's authority and, as a result, the agency has rendered more than 100 people from one country to another without legal proceedings and without providing access to the International Committee of the Red Cross, a right afforded all prisoners held by the U.S. military.

The CIA general counsel's office requires the station chief in a given country to obtain a verbal assurance from that country's security service. The assurance must be cabled back to CIA headquarters before a rendition takes place.

CIA Director Porter J. Goss told Congress a month ago that the CIA has "an accountability program" to monitor rendered prisoners. But he acknowledged that "of course, once they're out of our control, there's only so much we can do."

Asked to explain Goss's statement, an intelligence official said: "There are accountability procedures in place. For example, in some cases, the U.S. government is allowed access and can verify treatment of detainees." The official declined to elaborate.

Attorney General Alberto R. Gonzales said in an interview last week that, once a transfer occurs, "we can't fully control what that country might do. We obviously expect a country to whom we have rendered a detainee to comply with their representations to us. If you're asking me 'Does a country always comply?,' I don't have an answer to that."

In practice, though, the CIA has little control over prisoners once they leave CIA custody, said three recently retired CIA officials and other intelligence officials who have dealt with foreign intelligence services on detainee matters.

"These are sovereign countries," said Michael Scheuer, a recently retired CIA officer who favors the use of renditions to disrupt terrorist networks. "They are not going to let you into their prisons."

"Once they are in the jurisdiction of another country, we have no rights to follow up," said Edward S. Walker Jr., a former assistant secretary of state for Near Eastern affairs and now president of the Middle East Institute.

The U.S. official who visited foreign detention sites said the issue "goes far beyond" the assurance: "They say they are not abusing them, and that satisfies the legal requirement, but we all know they do."

For a country offering assurances, following up could imply the United States does not trust its leaders.

"We wouldn't accept the premise that we would make a promise and violate it," said the Egyptian ambassador to the United States, Nabil Fahmy, whose country has accepted rendered terrorism suspects. He denied that Egyptian officers employ torture in interrogations. "I don't accept the premise that if you want to torture someone, you send them to Jordan or Egypt. That would be the exception to the rule." Egypt, he added, "is becoming more and more rigorous" in prosecuting officers who use excessive force.

But Mamdouh Habib, an Australian citizen, has alleged he was tortured in Egypt for six months after U.S. officials sent him there. Habib had been detained in Pakistan in October 2001 as a suspected al Qaeda trainer. In Egypt, he alleges, he was hung by his arms from hooks, shocked, nearly drowned and brutally beaten. He was then sent to the U.S. military prison at Guantanamo Bay, Cuba, and was released in February.

Another Arab diplomat, whose country is actively engaged in counterterrorism operations and shares intelligence with the CIA, said it is unrealistic to believe the CIA really wants to follow up on the assurances. "It would be stupid to keep track of them because then you would know what's going on," he said. "It's really more like 'Don't ask, don't tell.' "

Questions about assurances have stalled the release of prisoners from Guantanamo.

Guarantees of humane treatment by Yemen notwithstanding, a federal court in the District of Columbia prohibited on Saturday the transfer of 13 Yemeni prisoners from Guantanamo to Yemen until a hearing is held on their attorneys' assertion that they could be tortured if returned there.

And despite assurances by China, State Department officials have been unwilling to send 22 Chinese Muslims from Guantanamo to China for fear they would be tortured.

Researcher Julie Tate contributed to this report.

At a news briefing, President Bush defended the practice of transferring suspected terrorists to countries of origin.