orge W. Casey Jr., the Army chief of staff, are said to be leaning toward a recommendation that steep reductions by the end of 2008, perhaps to half of the 20 combat brigades now in Iraq, should be the administration’s goal.

Such a drawdown would be deeper and faster than Gen. David H. Petraeus, the top commander in Iraq, is expected to recommend next month, administration officials said.

“If you’re out in Baghdad you might have a different priority for where you want the troops,” an administration official said, speaking on condition of anonymity because the White House has not authorized public remarks on the options being considered.

It has been known since the spring that the White House was considering options for reducing combat forces in Iraq by almost half in 2008, which could bring overall troop levels below 100,000. But the shape of the debate is only beginning to emerge.

President Bush will have to weigh whether such steep reductions in 2008, even if cast only as a goal, would risk eroding what a new National Intelligence Estimate has described as measurable but fragile security gains achieved in Iraq in recent months.

A Pentagon official who supports a sharp drawdown described the steep troop reductions as “what we’re shooting for, our initial goal.” The official said a drawdown to roughly 10 brigades would enable the Army to give many soldiers at least a year at home for every year they are deployed, an objective of Defense Secretary Robert M. Gates. Most soldiers are now serving 15 months in Iraq and get a year or less at home.

A combat brigade generally has around 3,500 soldiers, though some of the units in Iraq have as many as 1,000 additional troops.

With more than 160,000 troops now in Iraq, General Casey warned recently, “We’re consumed with meeting the current demands and we’re unable to provide ready forces as rapidly as we would like for other contingencies. He added, “This is a temporary state and one we must pass through quickly if we’re going to preserve and sustain our all-volunteer force and restore strategic depth.”

But the assessment that General Petraeus is preparing to deliver next month is likely to call for at most modest reductions in troop levels by next spring. At that point the five more brigades added this year under the president’s troop increase are likely to be withdrawn gradually.

Administration officials said Mr. Bush was acutely aware that some reduction next year would be required, and they said he planned to use next month’s debate to outline a plan for gradual troop reductions. He has not decided on a timetable or whether to go beyond pulling out the five additional brigades, officials said.

“At this point the only question is when the drawdown begins and how fast it proceeds,” said one senior administration official who has been deeply involved in the internal debate. “But to get there, something has to give.”

White House officials said Mr. Bush had yet to receive a formal proposal from General Pace or other officials about how large a troop withdrawal to make.

“The president has received no recommendation regarding our future force posture in Iraq,” Gordon D. Johndroe, a White House spokesman, told reporters in a briefing at Crawford, Tex. He was responding to a report in The Los Angeles Times that General Pace plans to advise Mr. Bush to reduce forces in Iraq by almost half by the end of next year.

In a statement, General Pace said he could not comment on what size withdrawal he would recommend. “I have not made or decided on any recommendations yet,” he said.

“I take very seriously my duty to provide the best military advice to the president,” he added. “I provide that advice privately to the president.”

With violence in Iraq expected to remain high into next year, it may be impossible for the United States to reach a force level of 10 brigades by late 2008, several Pentagon officials conceded. Mr. Bush and his commanders may decide on a less ambitious goal of reaching a force level of 12 to 15 brigades, and even that could be dependent on improvement in security conditions and in the Iraqi forces’ capabilities, they said.

What Mr. Bush announces next month may also be constrained to some extent by his warnings in recent months that publicizing a withdrawal could embolden the enemy in Iraq. He also has to take into account an assessment released this week by the nation’s intelligence agencies that cautioned that reducing forces too quickly could jeopardize recent security gains.

Complicating his decision-making further, Mr. Bush must balance the views of field commanders against those of members of Congress, who appear increasingly interested in seeing troop reductions this year.

In a briefing by video for Pentagon reporters on Friday, Maj. Gen. Rick Lynch, commander of the Third Infantry Division in Iraq, warned against starting to remove American troops later this year, an idea favored by many Democrats and endorsed this week by Senator John W. Warner, Republican of Virginia.

Mr. Warner, a longtime member of the Armed Services Committee, said Mr. Bush should announce a pullout of troops, even if only a small number, to press the Iraqi government to make political compromises.

“What would happen is the enemy would come back,” General Lynch said. “He’d start building the bombs again, he’d start attacking the locals again, he’d start exporting that violence to Baghdad. We would take a giant step backward.”

General Pace, who was not nominated for a second stint as chairman, is scheduled to retire at the end of September; presiding as the president’s senior military adviser over the next month’s review is likely to be his final major duty.

Whatever the Joint Chiefs recommend, it will have been coordinated with General Petraeus and with Mr. Gates in hopes of achieving a consensus, several Pentagon officials said.

When the decision was made late last year to send nearly 30,000 more troops to Iraq, General Pace served as an intermediary between the White House, which favored a large troop increase, and General Casey, the Iraq commander at the time, who wanted fewer, if any, additional troops. But now, as he prepares for retirement, General Pace may also feel emboldened to push for a faster withdrawal.

General Casey has long said that too large an American presence would deter the Iraqi government from assuming the lead role in securing the country. His views were largely rejected when General Petraeus was brought in, with a new strategy that called for using large numbers of American forces to protect Iraqis.

General Casey has used his new position, as Army chief of staff, to make clear his concerns that the elevated troop levels in Iraq are imposing too large a strain on the Army and his desire to do away with the current 15-month deployments in Iraq.

But some Pentagon officials said that General Casey, who traveled to Iraq and met with General Petraeus this month, still believed that the additional American forces, while helpful in reducing violence, slowed the Iraqi government’s maturation.

David S. Cloud reported from Washington, and Steven Lee Myers from Crawford, Tex.