The Senate voted without dissent yesterday to require the Bush administration to issue guidelines aimed at ensuring humane treatment of prisoners at U.S. military facilities and to report any violations promptly to Congress.

But, as it plunged into the controversy over abuse of detainees at Iraq's Abu Ghraib prison and whether interrogation methods were sanctioned by U.S. officials, the Senate balked at a Democratic proposal to bar interrogation by private contractors, who have been accused of involvement in the Abu Ghraib scandal.

It also rejected another Democratic proposal to make it a crime, punishable by as many as 20 years in prison and substantial fines, to engage in war profiteering. Instead, the Senate approved a Republican alternative extending two anti-fraud criminal statutes to cover overseas business operations.

In banning "cruel, inhuman and degrading" treatment of prisoners, the Senate was writing into law the policies that the administration has said it is following in accordance with the U.S. Constitution and international law. But the action also reflected concern over recently disclosed administration memos suggesting that the government may not be bound by these constraints in combating terrorism.

The proposal by Sen. Richard J. Durbin (D-Ill.), which was included in the defense authorization bill for next year, also went beyond current policy in requiring new rules to ensure compliance and disclosure of any violations to Congress.

Passage of the proposal by voice vote came after Republicans, facing defeat on the measure, agreed to raise no objections and offer no alternatives if the vote was taken by voice instead of putting all senators on record with a roll call, according to Democratic sources.

Durbin's proposal would require Defense Secretary Donald H. Rumsfeld to lay out guidelines for compliance within 180 days of the legislation's enactment. It would also require Rumsfeld to submit "on a timely basis and not less than twice each year" a report to Congress on any investigations of possible violations.

Final passage of the initiative is subject to negotiations with the House, which did not include similar language in its version of the defense bill.

The amendment to withdraw private contractors from interrogations after 90 days following enactment was defeated 54 to 43 after Republicans -- including some who expressed support for curtailing use of contractors -- objected that its provisions were too stringent and could seriously harm U.S. intelligence efforts.

Contractors have played a "significant" role in the abuse of prisoners and, unlike military personnel, may never be held accountable for their actions, said Sen. Christopher J. Dodd (D-Conn.), the proposal's sponsor.

But Armed Services Committee Chairman John W. Warner (R-Va.) said the Dodd proposal amounted to a "90-day jackhammer that severs our ability to continue our interrogation of prisoners with the use of contractors."

The profiteering amendment, proposed by Sen. Patrick J. Leahy (D-Vt.), was defeated, 52 to 46, after Republicans offered the fraud-statute alternative. Leahy described the alternative as the "hold Halliburton harmless" amendment -- a reference to the huge contracts in Iraq won by the company formerly headed by Vice President Cheney. But it was subsequently approved, 97 to 0.

Democrats argued that it would be more difficult to prosecute cases under fraud statutes than under a new law aimed specifically at "materially overvaluing" goods or services to profit "excessively" from war or reconstruction activities. Republicans contended it would be a mistake to change the basic law during a war.