President Bush's top defense advisers have recommended he maintain 15 combat brigades in Iraq until the end of the year contrary to expectations that the improved security in Iraq would allow for quicker cuts, The Associated Press has learned.

Military leaders told the AP that the closely held plan would send a small Marine contingent to Afghanistan in November to replace one of two Marine units expected to head home then.

If Bush follows the recommendations, he would delay any additional buildup in Afghanistan until early next year, when another brigade would be deployed there instead of to Iraq.

That move would cut the number of brigades in Iraq to 14 in February.

The plan is aimed at taking advantage of security gains in Iraq to bolster the military effort in Afghanistan, where violence is on the rise. Several senior military and defense officials described the recommendations on condition of anonymity because the plan has not been made public.

They also acknowledged the plan is a compromise since Gen. David Petraeus, the top U.S. commander in Iraq, argued to maintain the current force levels in Iraq — about 146,000 troops, including 15 combat brigades and thousands of support forces — through June.

Bush is weighing the recommendations; in the past, he has largely accepted the military's advice. If he adopts them, it would be left to the next president to execute further troop reductions in Iraq and a greater buildup in Afghanistan. Bush's term ends in January.

Democratic presidential nominee Barack Obama has advocated pulling all U.S. combat forces out of Iraqi within 16 months of taking office. GOP nominee John McCain has said he would rely on the advice of U.S. military commanders to determine the timing and pace of troop reductions. Both candidates have said more troops are needed in Afghanistan.

Obama said Thursday that the escalation of U.S. troops in Iraq, which he had opposed, has succeeded in reducing violence "beyond our wildest dreams."

But Iraq still has failed to achieve the political reconciliation and self-sufficiency that is required, he said, and he vowed to withdraw American troops and end the war.

Republicans repeatedly have accused Obama of denying the military progress being made in Iraq and of wanting to pull out when victory is within reach.

Campaigning in Pennsylvania, Obama was more effusive than usual in describing the reduction in violence that resulted largely from Bush's decision to send thousands of more troops to Iraq in 2007. But he stuck to his assertion that "the surge" has not led to the political reconciliation among quarreling factions that was its larger goal.

Defense Secretary Robert Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, are to testify before Congress on Iraq on Wednesday, suggesting that Bush will have announced his next move by then. Petraeus has given widely watched updates to Congress over the past year, assessing the effect of Bush's order to increase troops. He is not scheduled to testify before he leaves his post in mid-September.

Geoff Morrell, the Pentagon press secretary, said Thursday evening that Gates and Mullen had given Bush their recommendation on troop levels on Wednesday, while also presenting the views of Petraeus and other top military leaders. Morrell provided no details on the recommendation but said it reflected agreement among the senior Pentagon leadership "after serious and lengthy discussions" about recent security gains, as well as the security threats and uncertainties that remain in Iraq.

It had been widely expected that Petraeus would recommend a faster pullback in Iraq, perhaps calling for a reduction in the number of combat brigades from 15 to 14 this fall. But several recent events may have changed the calculus.

Among the more important changes was the unanticipated decision by Georgia to bring home its contingent of about 2,000 soldiers after Russia invaded the former Soviet republic in early August.

Also arguing in favor of a smaller reduction this fall was the inability of the Iraqi government to move ahead with provincial elections in October as originally planned. No firm date for the balloting has been set, but it is generally believed that the long-anticipated elections will not happen before December.

At the same time, however, military leaders have become increasingly concerned about escalating violence in Afghanistan, and they don't want to sit idle as the winter approaches, giving the enemy more time to build its forces.

One senior military official said it was considered critical to replace the Marines in Afghanistan beginning this year.

"We believe the risk in Afghanistan is such that we need to do something, and the risk in Iraq is such that we can go into Afghanistan without risking unduly the posture in Iraq," said the official.

Pentagon officials believe the greatest challenge is to identify enough support troops to provide essential logistics and intelligence assets for the additional U.S. units heading to Afghanistan.

Without that support — which includes the delivery of weapons and food and the construction of roads and runways — the fighting forces cannot be as effective.

Looking ahead, the Pentagon's plan would require a significant increase in military facilities in Afghanistan, including forward operating bases, like those in Iraq.

Pentagon leaders have struggled to balance the two warfronts, repeatedly stressing that Iraq is the priority.

On several occasions, Mullen has said that, "In Afghanistan, we do what we can; in Iraq, we do what we must."

But a resurgence of the Taliban in Afghanistan, coupled with the improved security in Iraq has forced a greater emphasis on Afghanistan.

Violence has plunged in Iraq's western Anbar province, which until early last year was a stronghold for the insurgency. That will allow a battalion of Marines — or roughly 1,000 — to go to Afghanistan to train security forces in November rather than going to Iraq as initially planned.

They would replace a Marine unit currently training Afghan security forces, but a second Marine unit now doing combat operations would not be replaced until early 2009, probably by an Army brigade.

There has been speculation that the 3rd Brigade, 10th Mountain Division, which is slated to go to Iraq, will instead go to Afghanistan. That unit, which is based at Fort Drum, N.Y., has previously served in Afghanistan.

Military leaders have insisted in recent months that over time they need to beef up forces in Afghanistan by as many as 10,000 troops — the equivalent of about three combat brigades.

More than 4,000 members of the U.S. military have died in the Iraq war since it began in March 2003.