BAGRAM AIR BASE, Afghanistan — Defense Secretary Robert Gates said today that U.S. commanders in Afghanistan have recommended an increase in U.S. force levels, in part to deal with an expected upsurge in Taliban violence this year.

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.

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 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.