Gates would not say how many more troops were recommended to him.
"It depends on different scenarios," he told reporters. "Those are the kinds of decisions we're going to have to look at."
Gates said U.S. troop levels in Afghanistan this year would depend in part on troop contributions from other NATO countries who are part of a U.S.-led coalition attempting to stabilize the country and prevent the Taliban from regaining power.
Noting a recent increase in Taliban attacks against U.S. and allied forces, Gates said the United States should "keep the initiative" and not allow the radical Taliban movement to regroup.
Gen. Peter Pace, chairman of the Joint Chiefs of Staff, did not mention any specific troop increase, but said it might make sense for "a short-term plus-up" if that would head off the potential need for even more in the years ahead.
Gates said the commanders' recommendation for a troop increase would be considered first by the joint chiefs and he would then decide what to recommend to President Bush.
A troop increase for Afghanistan would have the support of at least one likely Democratic presidential contender.
Sen. Hillary Rodham Clinton, D-N.Y., told CBS News' The Early Show Wednesday that while she is opposed to the president's plan to send more troops to Iraq, "I am for putting more troops in Afghanistan." (
Clinton recently returned from a trip to Iraq and Afghanistan where she held talks with U.S. military leaders.
Earlier, Gates had stood on a rocky dirt track ringed by 6,000-foot, snow-dappled ridges at Forward Operating Base Tillman as he came almost eye-to-eye with the source of the administration's worry about losing years of costly gains against the Taliban.
Gates, bareheaded and wearing a brown bomber jacket against the winter's chill at the bleak outpost, looked east into a part of Pakistan just a few miles away that has become an infiltration route for a growing number of Taliban fighters. U.S. military officials say they have evidence the Pakistani military has turned a blind eye to the border incursions.
Later, at a news conference, Gates acknowledged the border security problem and said something would have to be done about it. Only one month into his tenure at the Pentagon, Gates said he had not yet studied the issue in detail.
"The border area is a problem," Gates told reporters Tuesday after meeting with President Hamid Karzai. "There are more attacks coming across the border, there are al Qaeda networks operating on the Pakistani side of the border. And these are issues that we clearly will have to pursue with the Pakistani government."
Karzai acknowledged the upswing in Taliban attacks and vowed to deal them a heavy blow in the months ahead.
At Tillman, Sgt. 1st Class Ronald Locklear, who has spent five months there, said the problem is well-known.
"They cross the border on a regular basis," he said.
Gates noted that the Bush administration considers Pakistan an important ally in the global war on terrorism. U.S. military officials, however, stressed the impact of the Taliban's ability to find sanctuary in tribal areas on the Pakistan side of the border.
They said that allowed the Taliban to vastly increase the number of its attacks against U.S., NATO and Afghan army troops, particularly in the southern and eastern parts of the country where Osama bin Laden once operated.
The number of insurgent attacks is up 300 percent since September, when the Pakistani government put into effect a peace arrangement with tribal leaders in the north Waziristan area, along Afghanistan's eastern border, a U.S. military intelligence officer told reporters traveling with Gates. The officer discussed the matter on condition of anonymity.
Meanwhile, the top American commander in Afghanistan said he has asked to extend the combat tour of about 1,200 soldiers, amid rising insurgent violence, and Gates said he was "strongly inclined" to recommend a troop increase to President Bush if commanders believe it is needed to succeed.
The prospect of a troop increase, at the same time Mr. Bush is ordering 21,500 more troops into Iraq, raises new questions about the military's ability to sustain its pace of war-fighting on two major fronts. There now are about 24,000 U.S. troops in Afghanistan, which Lt. Gen. Karl Eikenberry said is the highest since the war began in October 2001.
It also raises questions about the future course of the war in Afghanistan, which the United States is increasingly handing off to NATO forces. Of the 31,000 troops here under NATO command, about 11,000 are American. The United States has another 12,000 or 13,000 under U.S. command to hunt down al Qaeda terrorists and train the Afghan army.
Eikenberry, the senior American commander here, told reporters he has recommended to the Pentagon that 1,200 soldiers from the 2nd Battalion, 30th Infantry Regiment, 10th Mountain Division — which is about halfway through a scheduled four-month tour in eastern Afghanistan — be ordered to stay through year's end. Eikenberry is due to leave his post Jan. 21.
That battalion is already scheduled to deploy to Iraq later this year, an illustration of how stretched U.S. forces are by the two wars.
Eikenberry said it appears the Taliban is readying a spring offensive to focus mainly on southern Afghanistan, particularly in the city of Kandahar and other urban centers. He also said he believed the Taliban would make renewed efforts to "get inside Kabul" and to attack border posts held by NATO and Afghan national forces.
He asserted that despite the Taliban's resurgence, "The enemy is not strong militarily. A lot of this has to do with the attempt to get psychological effects" to persuade ordinary Afghans the U.S.-backed government cannot deliver necessary services, Eikenberry said.