WASHINGTON -- As deadly new guerrilla attacks rocked the U.S.-led occupation, President Bush shifted policy on Iraq's political future yesterday, approving ideas for turning power over to a provisional government by the summer or fall of 2004.

After two days of urgent meetings at the White House, Bush and his national security team approved an accelerated plan for elections intended to show Iraqis a "movement away from occupation" and to give them "a stake in running their own country," an administration official said.

But while Iraqis would gain more political power, U.S. administrator L. Paul Bremer III is likely to retain a veto on Iraqi government decisions, and the United States has no intention of withdrawing troops until security is restored in Iraq, officials said.

The new proposals mark the beginning of what one administration official called an "exit strategy" as Bush heads into an election year. They replace the original U.S. seven-step plan requiring Iraqis to approve a constitution before the election of a government.

Although the date for elections is uncertain, possibly three to four months from now, several officials said the new plan aims to have a provisional government installed by summer. But they said the timetable could be delayed until fall or even to early 2005. The proposals will be put before the U.S.-appointed Iraqi Governing Council.

The new proposals draw from political transitions in Afghanistan, which has an interim government, and Bosnia, where an international administrator wields veto power.

A plan like the Afghanistan model was advocated months ago by United Nations Secretary-General Kofi Annan but rejected by the Bush administration in favor of having the U.S.-led Coalition Provisional Authority, headed by Bremer, remain in charge while it guided Iraq's political transition.

The U.S. proposals call for some members of a new provisional government to be elected and others appointed. A prime minister may be appointed from among existing government ministers.

Soon after government elections, a second vote would be held to pick members of a commission to draft a constitution.

The proposals would give the Iraqi government power to develop and implement policy and not just endorse decisions by Bremer, one official said.

The policy shift amounts to a tacit admission that Bush's strategy - of keeping a firm U.S. grip on power in Iraq during a long political process - isn't working. It reflects the administration's growing view, underscored by a gloomy CIA assessment, that with the visible American control of power in Iraq, average Iraqis won't cooperate in restoring security and rebuilding the country unless they are convinced that the occupation will end fairly soon.

Iraq's spreading guerrilla war took a heavy toll yesterday with a truck bombing in the southern Iraqi town of Nasiriyah that killed at least 27 people, including 18 Italians and nine Iraqis. The blast was the first fatal attack on the Italian contingent, which contributes military police and soldiers to a European occupation force led by Britain. Until yesterday, Shia-dominated Nasiriyah appeared to be largely free of the insurgency battling occupation forces in the northern Sunni areas.

The growing violence isn't the only problem U.S.-led forces face. Iraqis have been reluctant to cooperate fully until they get a sense of when the U.S. occupation will end and Iraqis will control their country, officials said. Meanwhile, they are subject to intimidation by remnants of Saddam Hussein's fallen regime, officials said.

"Right now, if you walked down a street [in Iraq] and said, 'What's the long-range plan for democracy?' people would be hard-pressed to say what it is," a senior administration official said.

Administration officials are also growing frustrated with the slow pace shown by the Iraqi Governing Council in assuming responsibility for running the country. Members of the council are described by some officials as putting their business or tribal interests ahead of governing.

The council faces a deadline from the U.N. Security Council to come up with a timetable by Dec. 15 for drafting a constitution and scheduling elections. But the process has stalled, U.S. officials say, and the two days of White House meetings were intended to revive it.

The meetings included Bremer, hastily summoned from Iraq this week; Vice President Dick Cheney; Powell; Defense Secretary Donald H. Rumsfeld; and National Security Adviser Condoleezza Rice.

Bremer stressed yesterday that the final decision on moving forward with the accelerated political plan would be left up to the council. Showing deference to the 24-member body, he declined to detail the U.S. proposals - which he said were developed in conjunction with the council - before conferring further with council members.

"They're not my options; they're options put forward by the governing council," he told reporters outside the White House after yesterday's meeting. "I will now go back [to Baghdad] and reflect the president's and his advisers' views on the path forward."