WASHINGTON - President Barack Obama will review a new U.S. military report on Afghanistan this week and any decision on changing the U.S. presence there is weeks away, Obama's spokesman said on Tuesday.

Obama would take some form of the report by U.S. Army Gen. Stanley McChrystal with him when he leaves on Wednesday for Camp David, where he will spend the rest of the week on vacation, spokesman Robert Gibbs told reporters.

The confidential report by the commander of U.S. and NATO forces in Afghanistan has been described by officials as an assessment of the situation on the ground and does not include specific requests for more U.S. troops. Such a request could come later.

I'm told we don't expect resource decisions or requests for several weeks, Gibbs said.

There is a debate within the Obama administration over whether to send more U.S. troops to Afghanistan at a time when public support for the eight-year-old war is eroding.

McChrystal submitted his report to the Pentagon on Monday.

A CBS News poll released on Tuesday said four in 10 Americans surveyed said they want U.S. troop levels in Afghanistan decreased, a percentage which has been rising since the beginning of 2009.

The poll found that less than half, 48 percent, of those questioned said they approved of Obama's handling of the situation in Afghanistan, down from 56 percent in April.

McChrystal has about 103,000 troops under his command, including 63,000 Americans, half of whom arrived this year as part of an escalation strategy started by former President George W. Bush and ramped up under Obama.

The force is set to rise to 110,000, including 68,000 Americans, by year's end.

(Reporting by Steve Holland, Editing by Frances Kerry)