WASHINGTON - A request from the top U.S. and NATO commander in Afghanistan for additional troops has been transferred to President Barack Obama for review and has started working its way through the military chain of command, the Pentagon said on Wednesday.

The request, which General Stanley McChrystal submitted to Defense Secretary Robert Gates last month, recommends adding up to 40,000 additional U.S. and NATO troops next year, according to congressional officials.

Obama, who has launched a review of his six-month-old counterinsurgency strategy in Afghanistan, has not decided on whether to send more troops as recommended by McChrystal to try to reverse gains by a resurgent Taliban, officials said.

Sending as many as 40,000 additional troops to Afghanistan could spark a backlash within the president's own Democratic Party. U.S. and NATO casualties have risen, and public support for the eight-year-old war has eroded.

The president requested it, the secretary provided it to him as well as to the principals, and now it is working its way up the formal chain of command, here and in NATO, Pentagon press secretary Geoff Morrell told reporters.

He described the request, which Gates gave to Obama late last week, as informal because it had yet to work its way through the chain of command, a process that allows for vetting and comments from commanders.

Morrell said Obama asked for a copy of the troop request because he wanted to read this over the weekend.

Morrell said it remained unclear when McChrystal's request would be discussed as part of the White House review of its strategy in Afghanistan and Pakistan.

'A RANGE OF OPTIONS'

A meeting was scheduled for later on Wednesday focusing on Pakistan. Another meeting on Friday is expected to deal primarily with Afghanistan.

This is a more analytical document, as it's been described to me, which would offer a range of options but would ultimately provide one recommendation, Morrell said of McChrystal's troop request.

He added that the request was based upon the assumption that we were pursuing a counterinsurgency strategy in Afghanistan.

If the decisions that are made in the coming weeks are different from that, there can be adjustments made to the request, he said.

The Pentagon says Gates, who could sway Obama in favor of sending more troops, has yet to decide on whether they are needed.

But Gates publicly has said that many of his earlier reservations about adding forces have been addressed, and he remains a strong proponent of a counter-insurgency strategy -- signals that he may be leaning toward a further buildup.

(Reporting by Adam Entous and Phil Stewart; Editing by Will Dunham)

Pakistan Barack obama Afghanistan