“The overall situation in Afghanistan probably will deteriorate modestly this year in the face of persistent political instability, sustained attacks by the Taliban-led insurgency, unsteady Afghan National Security Forces performance, and chronic financial shortfalls,” Dan Coats, the director of national intelligence, told the United States Senate last week.

Mr. Coats said Afghan forces “probably will maintain control of most major population centers with coalition force support, but the intensity and geographic scope of Taliban activities will put those centers under continued strain.”

President Trump, under his new strategy for the region, has expanded the presence of American military advisers in Afghanistan by a few thousand troops, making more available to work with the Afghan forces at a smaller unit level.

Capt. Tom Gresback, a spokesman for the United States military in Afghanistan, said new specialized units were arriving to assist Afghan forces at the battalion level across the country. Already, about 800 such service members — many of whom have done previous tours in Afghanistan and have received specific training for this kind of mobile advisory mission where they will be sent from one part of the country to the next — have arrived.

“We are in the process of deploying them throughout the country,” Captain Gresback said.

Officials in northern Afghanistan said that already more American advisers were arriving to help in the battle.

Said Sarwar Hussain, a spokesman for the Afghan police in the north of the country, said a unit of about 300 American special forces would be based in the restive province of Faryab.

“They will advise in our operations and assist with air power,” Mr. Hussaini said, adding that “120 of them have arrived by air, and the rest are waiting for the main highway to be cleared before they go to Faryab.”