The Bush administration has launched a top-level lobbying campaign to persuade skeptical U.S. lawmakers and disapproving Iraqi politicians to support a security agreement governing the continued presence of American troops in Iraq.

Although congressional approval is not legally required, U.S. lawmakers' support is considered crucial for an agreement to go forward. In Iraq, where the deal must pass through several complex layers of approval, the going is considered even tougher.

Secretary of Defense Robert Gates, Secretary of State Condoleezza Rice and Bush's national security adviser, Stephen Hadley, are among those reaching out to key members of the House and Senate. Rice also is pressing senior Iraqi leaders to accept the deal.

The agreement includes a timeline for U.S. withdrawal by 2012 and a crucial but unpopular compromise that gives Iraq limited ability to try U.S. contractors or soldiers for major crimes committed off-duty and off-base, officials said Thursday.

The campaigns of Democratic presidential nominee Barack Obama and Republican rival John McCain, both on Senate committees that deal with the issue, have been briefed on the draft, although neither candidate has signaled a position publicly. In their debate Wednesday, McCain made only a fleeting reference to it. "We're now about to have an agreement for status of forces in Iraq coming up," he said, without further comment.

Rice on Wednesday called senior Iraqi leaders, pressing them to accept the deal that contains elements that many in Baghdad see as a violation of their country's sovereignty, officials said.

"The Iraqis are considering the text, we are talking to the Iraqis," State Department spokesman Sean McCormack said. He said Rice had spoken to Iraqi President Jalal Talabani, Prime Minister Nouri al-Maliki and Vice President Adil Abdul-Mahdi, a Shiite and a top member of the Supreme Council.

A statement from Abdul-Mahdi's office said he and Rice discussed "ways to promote the agreement in line with the interests of the Iraqi people and to guarantee all their rights." Abdul-Mahdi also met personally on Thursday with U.S. Ambassador to Iraq Ryan Crocker, officials said.

U.S. officials said Rice and Crocker told the Iraqis that the agreement is critical for future U.S.-Iraq relations and that it is the final offer the administration is willing to make. The officials spoke on condition of anonymity to discuss private diplomatic conversations.

The administration's greatest concern for the deal's future involves not the U.S. Congress but Iraq's fractured internal political system. There is some pessimism in Washington that the agreement will survive the Iraqi approval process.

The administration had hoped to conclude the agreement by the end of July, to leave plenty of time to sell it before the current U.N. mandate for the U.S.-led international force in Iraq expires on Dec. 31. Now it has less than three months to go before that legal cover for U.S. forces disappears.

The U.N. mandate could be extended, but that could be a difficult process, and is a route neither the Iraqis nor the U.S. relish pursuing.

Without either a deal or an extension, the worst-case scenario is that U.S. troops in Iraq would have to be confined to their barracks.

Congress is not in session and it was not clear Thursday how many members had been contacted. The message Bush aides are delivering is that the deal is the best U.S. negotiators were able to get from the Iraqis under current political circumstances there, the officials said.

The administration always expected the legal jurisdiction issue to be the most difficult in the negotiations. Some U.S. lawmakers have deep concerns about allowing Iraq's fledgling judicial system to have even limited authority over American soldiers. Pentagon officials also have expressed concern.

But Pentagon press secretary Geoff Morrell said Thursday that Gates accepts the agreement and is calling senior members of the House and Senate armed services committees to explain the details.

"I don't think the secretary would be making phone calls in support of the document if he didn't believe it adequately protected our forces in Iraq," Morrell said. "He is comfortable with the document that he is calling people about today."

Morrell would not provide details of the draft, but acknowledged there are withdrawal timelines. He said those dates "are goals that ... will only be followed if the conditions on the ground provide for it."

Other provisions of the draft give Iraqis a far greater role in U.S. military operations than at any time during the nearly six-year war. American troops would no longer be allowed to detain suspects or search homes without Iraqi legal authorization except in active combat. In addition, anyone detained by the Americans must be handed over to the Iraqis within 24 hours, and all detainees currently held by the U.S. must be released or transferred to Iraqi control.