The security agreements between Iraq and the United States mark the beginning of the end of the war. They are only the beginning, though, and the terms of the agreements create uncertainties that could disrupt the smooth withdrawal of American troops from Iraq.

The agreements — a broad “strategic framework” and a more detailed security pact that were ratified Thursday by the Iraqi Parliament — set a deadline that critics of the war have long wanted. They require that all American forces withdraw from Iraq no later than Dec. 31, 2011, but they offer no timetable for withdrawals, and in theory could add three more years to a war that has already lasted five and a half.

The United States has also agreed to remove all combat forces from Iraqi cities and villages by the end of next June, though the agreements remain silent on what constitutes “combat” troops and where exactly they will move. Those decisions have been left to a Joint Military Operations Coordination Committee, a body of Americans and Iraqis that could prove to be as ungainly as its acronym, Jmocc.

The committee will have the authority to approve American military operations; the use of bases and facilities; the detention of Iraqis by American forces; and even — in rare cases, it would seem — the prosecution of American troops accused of “grave premeditated felonies” committed while off duty and off base. Any number of circumstances could strain cooperation and even lead to conflict.

“Question marks remain in the agreement concerning freedom of action for U.S. soldiers, vague security commitments and protection of Iraqi assets,” Travis Sharp, a defense analyst at the Council for a Livable World, a nonprofit advocacy group, wrote in a statement after the Iraqi Parliament voted.

The council has long opposed the war, but it was telling that it expressed support for the agreements. The reason is that the vagueness of some of the terms and definitions also gives President-elect Barack Obama a fair amount of flexibility to carry out his campaign promises to end the war.

That opponents of the war support the agreements is a victory for President Bush, albeit a mixed one. It is also a vindication of Mr. Obama’s insistence on establishing a timetable to withdraw, forcing the Americans and the Iraqis to contemplate a time without foreign troops occupying the country.

Already American commanders have begun considering how to accelerate withdrawals of combat brigades on a schedule much closer to Mr. Obama’s than seemed possible a year ago. At the same time, the agreements leave room for keeping in place a larger contingent than Mr. Obama’s supporters might have envisioned, with tens of thousands of American troops remaining in training and other support roles at least for the time being.

Brooke Anderson, a policy adviser and spokeswoman for Mr. Obama’s transition team, welcomed Iraq’s approval of the agreements, saying that the Obama team was “encouraged to see progress” in establishing the conditions for an American presence beyond the expiration of the United Nations mandate at the end of the year.

The reason the agreements are a victory for Mr. Bush is that his administration has effectively negotiated an end to a costly and widely unpopular war that was begun in 2003 with a rationale — eliminating Iraq’s unconventional weapons — that has since been discredited.

In the waning months of his presidency, Mr. Bush had to drop his initial opposition to any firm deadlines for American withdrawal, as Mr. Obama urged on the campaign trial, and agree to Iraqi demands to have a greater and greater say in the country’s governance in the meantime.

“Given where we were in January 2007, we have seen an almost unthinkable pace of progress on political, economic and security issues,” Mr. Bush’s spokesman, Gordon D. Johndroe, said in a statement, describing the agreements as evidence of the success of the president’s strategy. “So much so that the improved conditions allowed us to come to this mutual agreement with a sovereign Iraq that is solving its problems in the political process, not with guns and bombs.”

The concessions that Mr. Bush accepted to Iraqi sovereignty have raised concerns among prominent Democrats in Congress, including Senator Carl Levin of Michigan, the chairman of the Armed Services Committee, and his counterpart in the House, Representative Ike Skelton of Missouri.

But any withdrawal from Iraq was inevitably going to accompany stronger assertions of Iraqi sovereignty and thus an uncertain period of transition in which real operational control passes from the American military to Iraq’s.

Article 9 of the agreement governing security forces, for example, gives Iraq control of its airspace for the first time since the war began but goes on to say that Iraq may request “temporary support” from the United States.

Still unclear is how many American forces are expected to remain between now and the deadline for withdrawal, and whether any could stay beyond then. What is clear is that beginning on Jan. 1, when the agreements go into effect, American-led operations in Iraq will be conducted under far greater restraints.

The history of the war suggests that security gains are reversible, that whatever political reconciliation unfolds will be punctuated by eruptions of violence, that American forces will continue for some time to oversee an ethnic and sectarian patchwork that could quickly revert to civil war.

As part of the effort to win passage from Iraq’s Parliament, the government of Prime Minister Nuri Kamal al-Maliki also agreed to hold a national referendum next year on the agreements. A vote against them would put the American forces then in Iraq — almost certainly more than 100,000 troops — in a legal limbo without the United Nations mandate the agreements are intended to replace at the end of this year.

“It is quite apparent that the Bush administration will be leaving the Obama administration with a messy, complicated and unstable situation in Iraq,” the National Security Network, a policy group made up mostly of Democrats who have sharply criticized Mr. Bush’s policies, said in a statement.

It has also left Mr. Obama a way out.