WASHINGTON — Worried about a growing threat from the Islamic State in Libya, the United States and its allies are increasing reconnaissance flights and intelligence collecting there and preparing for possible airstrikes and commando raids, senior American policy makers, commanders and intelligence officials said this week.

While no decision has been finalized about when the United States and its allies will formally expand action in Libya against the Islamic State, also known as ISIS or ISIL, administration officials indicated that it might be very soon. A decision will probably come in “weeks” but “not hours,” Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, said Friday.

“It’s fair to say that we’re looking to take decisive military action against ISIL in conjunction with the political process” in Libya, General Dunford said. “The president has made clear that we have the authority to use military force.”

United States and British Special Operations teams have for months been conducting clandestine reconnaissance missions in Libya to identify militant leaders and map out their networks. Separate teams of American Special Operations forces have over the past year been trying to court allies from among a patchwork of Libyan militias that remain unreliable, unaccountable, poorly organized and divided by region and tribe.