BAGHDAD - Iraqi officials stepped up pressure on the United States on Tuesday to agree to a timeline to withdraw American forces, a sign of the government's growing confidence as violence falls.

The tough words come as the Bush administration is running out of time to reach a needed troop deal before the U.S. election in November and the president's last months in office. Some type of agreement is required to keep American troops in Iraq after a U.N. mandate expires Dec. 31.

The Iraqi timeline proposal made public Tuesday appears to set an outer limit, requiring U.S. forces to fully withdraw five years after the Iraqis take the lead on security nationwide -- though that precondition could itself take years.

"Our stance in the negotiations under way with the American side will be strong," said Iraq's national security adviser, Mouwaffak al-Rubaie, a day after the country's prime minister first publicly said he expects some type of timeline.

"We will not accept any memorandum of understanding that doesn't have specific dates to withdraw foreign forces from Iraq," al-Rubaie told reporters.

President Bush has said he opposes a timeline. The White House said Monday that it did not believe Prime Minister Nouri al-Maliki was proposing a rigid timeline for U.S. troop withdrawals.

In Washington, the State Department declined to comment specifically on al-Rubaie's remarks, saying it would not negotiate the agreement in public. But it reiterated that the United States fully intends to withdraw troops from Iraq when conditions are appropriate to do so.

"We want to withdraw. We will withdraw. However, that decision will be conditions-based," said Gonzalo Gallegos, a State Department spokesman. "We're looking at conditions, not calendars here."

"We're making progress and are committed to departing, as evidenced by the fact that we have transferred over half of the country's provinces to provisional Iraqi control, and we're planning on removing the fifth and final surge brigade at the end of the month here, if things go according to plan," he told reporters.