WASHINGTON, Sept. 21 — The Bush administration and Congressional Republicans reached agreement Thursday on legislation governing the treatment and interrogation of terrorism suspects after weeks of debate that divided Republicans heading into the midterm elections.

Under the deal, President Bush dropped his demand that Congress redefine the nation’s obligations under the Geneva Conventions, handing a victory to a group of Republicans, including Senator John McCain of Arizona, whose opposition had created a showdown over a fundamental aspect of the rules for battling terrorism.

The administration’s original stance had run into fierce resistance from former and current military lawyers and Mr. Bush’s former secretary of state, Colin L. Powell, a former chairman of the Joint Chiefs of Staff. They argued, as did Mr. McCain and the other two senators leading the resistance, that any redefinition would invite other nations to alter their obligations and endanger American troops captured abroad.

“There is no doubt that the integrity and the letter and the spirit of the Geneva Conventions have been preserved,” said Mr. McCain, who was tortured during more than five years as a prisoner in North Vietnam.

Members of Congress and administration officials announced the deal after emerging from a tense and intricate all-day meeting in Vice President Dick Cheney’s office in a Senate building. They said they would try to push the measure through in the five days Congress is scheduled to meet before lawmakers leave to go out and campaign.

The White House moved quickly to assert that it had not surrendered. Administration officials characterized the negotiations as cooperative and the result as a victory for all sides.

“The agreement clears the way to do what the American people expect us to do: to capture terrorists, to detain terrorists, to question terrorists, and then to try them,” Mr. Bush said in Orlando, Fla., where he was attending fund-raisers for several Republican candidates.

The dispute revolved around how to define the rules governing the interrogations of terrorism suspects and providing legal protection to C.I.A. officers conducting interrogations. Under the deal, Congress would seek to codify the limits by outlining in the War Crimes Act, a domestic law, several “grave breaches” of the relevant provision of the Geneva Conventions, known as Common Article 3. The deal would eliminate a legislative provision in the original White House proposal saying that compliance with the Detainee Treatment Act, which Congress passed last year and which bans “cruel, inhuman or degrading treatment,” would by itself satisfy the obligations of the United States under the conventions.

“Everybody agreed we ought to try and do it in a way that did not involve modifying or amending our international obligations,” said Stephen J. Hadley, the president’s national security adviser. “That was the objective we all came to here in the last week. The goal was whether we could find language mutually agreed between the Senate and the White House that would achieve those objectives.”

Dan Bartlett, counselor to the president, said: “We proposed a more direct approach to bringing clarification. This one is more of the scenic route, but it gets us there.”

The agreement says the executive branch is responsible for upholding the nations’ commitment to the Geneva Conventions, leaving it to the president to establish through executive rule any violations for the handling of terrorism suspects that fall short of a “grave breach.” Significantly, Senate aides said, those rules would have to be published in the Federal Register.

The agreement provides several pages describing “grave breaches” that would not be allowed, starting with torture and including other forms of assault and mental stress. But it does not lay out specific interrogation techniques that would be prohibited.

The adjustment to the War Crimes Act, “will put the C.I.A. on notice of what they can and can’t do,” said Senator Lindsey Graham of South Carolina, who, along with Senator John W. Warner of Virginia, joined Mr. McCain in leading resistance to the White House approach. “It would take off the table things that are not within American values.”

Asked about one of the most controversial interrogation techniques, a simulated drowning known as water-boarding, Mr. Graham said, “It is a technique that we need to let the world know we are no longer engaging in.”

Gen. Michael V. Hayden, the C.I.A. director, issued a statement to employees, saying, “If this language becomes law, the Congress will have given us the clarity and the support that we need to move forward with a detention and interrogation program that allows us to continue to defend the homeland, attack Al Qaeda and protect American and allied lives.”

The senators were careful not to characterize winners and losers. “This was a give-and-take,” Mr. Graham said.

The senators agreed to a White House proposal to make the standard on interrogation treatment retroactive to 1997, so C.I.A. and military personnel could not be prosecuted for past treatment under standards the administration considers vague.

Senators Graham McCain and Warner said the agreement met the three goals they set from the beginning: to preserve the Geneva Conventions, to allow the C.I.A. to continue interrogations and to set up a program that would pass court review.

On another point of contention, the use of classified evidence in prosecutions of terror suspects, the senators won agreement that suspects would be allowed to see any evidence the jury sees, which the senators say is in keeping with 200 years of American judicial tradition. But the agreement includes procedures that would strip the evidence of the most sensitive details that lawmakers have worried could be used to plan more attacks.

The agreement would not allow any evidence obtained by techniques that violate the Detainee Treatment Act, and would not allow hearsay evidence that the defense successfully argues is not reliable or probative.

The Supreme Court had thrown the issue to Congress in June, when it struck down the tribunals the president established shortly after the terror attacks of Sept. 11, 2001, saying they violated constitutional and international law.

After weeks of standoff over proposed legislation, the two sides had begun to negotiate in earnest in the last few days, after Mr. Hadley said on the Sunday morning news programs that he believed they could reach consensus without modifying international agreements.

Thursday morning, Senator Bill Frist of Tennessee, the majority leader, who has supported the president’s approach, told Mr. Warner that with just a week left before the Senate is to adjourn, they needed a deal by evening.

Mr. Frist said he would send the bill to the floor. In the House, Representative Duncan Hunter of California, chairman of the Armed Services Committee, said he had some concerns about the use of classified evidence, but added, “I think we’re very close.”

Democrats have put their trust in Senators Graham, McCain and Warner to push back against the White House, and Thursday they signaled that they intended to continue cooperating. “Five years after Sept. 11, it is time to make the tough and smart decisions to give the American people the real security they deserve,” said the Democratic leader, Harry Reid of Nevada.

Still, Senator Carl Levin of Michigan, the senior Democrat on the Armed Services Committee, said he would press to change a provision in the proposal that would deny detainees a right to challenge their captivity in court.

Annotazioni − Sheryl Gay Stolberg contributed reporting.