Defense Secretary Robert Gates suggested on Wednesday that he is likely to urge President Bush to send more troops to Afghanistan to fight the resurgent Taliban.

Gates said U.S. commanders in Afghanistan have recommended an unspecified troop boost, and while he did not explicitly endorse the idea, he offered a rationale.

"I think it is important that we not let this success here in Afghanistan slip away from us and that we keep the initiative," he told reporters traveling aboard his aircraft as it refueled here for a flight to Riyadh, Saudi Arabia, where he was to meet with King Abdullah. "There's no reason to sit back and let the Taliban regroup," Gates said.

There are approximately 24,000 U.S. troops here, of which about 11,000 serve under NATO command. Another increase would raise questions about the future course of a war in which the United States is increasingly handing off to NATO forces.

As described by U.S. military officers in Afghanistan, the Taliban already have regrouped, at least to the extent that they were able last year to launch vastly more attacks on U.S. and allied forces than in 2005. They have been particularly resurgent in the south and the east, along the Pakistan border.

Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said new troop commitments would further strain the U.S. military in the short run. But if done as part of a successful strategy against the Taliban, it might hasten the day when the U.S. military can withdraw its combat forces altogether, he said.

Pace arrived separately in Afghanistan to join Gates for his meetings. They were going to fly together Wednesday to Kandahar, in southern Afghanistan, but weather forced their plane back to Bagram, where Pace boarded a C-17 cargo plane to return to Washington. Gates then flew to Riyadh in another C-17.

A U.S. troop increase in Afghanistan would come on top of Bush's decision to send another 21,500 soldiers and Marines to Iraq over the coming four months. The two wars, each now longer than U.S. involvement in World War II, have stretched American land forces so thin that the Army and Marines are requesting tens of billions more in funding and have persuaded Bush to ask Congress to increase their size.

On Tuesday, Gates said before he arrived in Afghanistan for talks with U.S. and NATO commanders — as well as Afghan government officials — that he wanted to hear their views on what should be done to arrest the resurgence of the Taliban and provide the security needed to reconstruct the country.

U.S. forces invaded Afghanistan to topple the Taliban regime in October 2001. No longer a sanctuary for terror mastermind Osama bin Laden, Afghanistan has struggled to build a national government, attract international investment and rid the country of Taliban extremists who want to regain power.

"If the people who are leading the struggle out here believe that there is a need for some additional help to sustain the success that we've had, I'm going to be very sympathetic to that kind of a request," Gates said.

Asked directly by a reporter whether such a request had been made, Gates said yes but offered no details. The number of extra troops, he said, "depends on different scenarios," which now will be examined.

He said the Joint Chiefs of Staff — the top uniformed officers of the Army, Navy, Marine Corps and Air Force — will discuss this with Pace, and then Gates will decide what to recommend to Bush. It was not clear how long this might take.

"I think we have the forces" needed to expand the military commitments in both Iraq and Afghanistan, Gates said. "What we have to look at is what the impact is if we were to add more forces here. Ultimately, obviously, it would be the president's decision."

Altogether, there now are about 24,000 U.S. troops in Afghanistan, including the roughly 11,000 under NATO command. The top commander, Lt. Gen. Karl Eikenberry, said in an interview Tuesday that this was the highest total since the war began.

Eikenberry said he has asked the Pentagon to order a battalion of the 10th Mountain Division to remain in Afghanistan until the end of the year rather than leave this spring. The unit already is scheduled to deploy to Iraq later this year — an example of how thinly stretched the military has become.

It was not clear how many other troops have been requested for Afghanistan. The U.S. military has about 3,500 troops at Bagram Air Base, which is a hub for air supply operations and is the headquarters of the main U.S. contingent in the country, a brigade of the 10th Mountain Division from Fort Drum, N.Y.

The rest of the U.S. troops are largely in the east, along the Pakistan border, and in the south as part of the NATO-directed force.

In addition to the U.S. force, NATO has about 20,000 troops around the country. The prospect of a U.S. troop increase presents a possible form of leverage for Washington, which is pressing NATO to provide roughly 3,000 troops which it pledged last year but has not yet delivered.

Gates said he will be pushing NATO countries to fulfill that pledge in coming weeks.