INCIRLIK AIR BASE, Turkey — Defense Secretary Leon E. Panetta signed an official deployment order on Friday to send 400 American military personnel and two Patriot air defense batteries to Turkey as its tensions intensify with neighboring Syria, where government forces have increasingly resorted to aerial attacks, including the use of ballistic missiles, to fight a spreading insurgency.

The American batteries will be part of a broader push to strengthen Turkey’s defenses that will include the deployment of four other Patriot batteries — two from Germany and two from the Netherlands. Each battery contains multiple rounds of guided missiles that can intercept and destroy other missiles and hostile aircraft flying at high speeds.

Mr. Panetta’s deployment order, the result of NATO discussions last week, represents the most direct American military action so far to help contain the Syrian conflict and minimize its risk of spilling across the 550-mile border with Turkey, a NATO member that is housing more than 100,000 Syrian refugees and providing aid to the Syrian rebels trying to oust President Bashar al-Assad.