KABUL, Afghanistan - The U.S. military is seeing early signs that al-Qaeda might be stepping up its activities in Afghanistan, a senior defense official revealed yesterday as Secretary Robert M. Gates made his third trip to the country.

Gates said he had not yet seen data on any uptick in al-Qaeda activity, but he said increasing levels of violence in the country were a concern and he would talk about it with other NATO defense leaders operating in Afghanistan.

"I'm not worried about a backslide as much as I am how we continue the momentum going forward," Gates told reporters in Djibouti yesterday before he left for Kabul. "One of the clear concerns that we all have is that in the last two or three years, there has been a continuing increase in the overall level of violence."

The senior defense official said the U.S. military was concerned and was looking for definitive signs of greater activity by al-Qaeda and foreign fighters, but the United States had not seen enough proof to draw any final conclusions. The official discussed the terrorist network on condition of anonymity because of the security concerns.

As Gates headed to Kabul, U.S. officials also said they were considering the possibility of providing arms to local tribes in Afghanistan, along with training, equipment and other support. The effort would be modeled after successful efforts in Iraq to empower the locals to police their own neighborhoods.

While no decisions have been made, officials said the plan was under review.

The U.S. military has been pushing the idea that more attention must be paid to tribal leaders in the provinces in both Afghanistan and Iraq, rather than focusing all the attention on buttressing the central governments of those two nations. The thinking is that the locals are closer to the community and their people, and thus can better police their own streets.

Military officials have said they believe that the Taliban in Afghanistan is being refueled, possibly by extremists in Pakistan crossing the border, or through support from other countries in the region sympathetic to the extremists.