WASHINGTON — The Air Force wants to bolster the budget for its deadliest drones by more than 60 percent, reflecting increasing demand for unmanned planes to track and kill insurgents in Iraq and Afghanistan, according to documents and a top combat commander.

The Air Force is seeking $540 million for Predator and Reaper aircraft, up from $334 million in 2008. The remotely controlled planes' ability to linger over a target as long as a day, provide images of insurgent activity and fire weapons to kill them is changing the nature of combat.

"What we're able to get with our Predators and our Reapers is persistence," said Lt. Gen. Gary North, who runs air combat operations across Africa and parts of Asia, including Afghanistan. "With the Reaper we get an increased lethality."

Defense Secretary Robert Gates, who has seen the unmanned planes in Iraq and watched them piloted remotely from Nevada, has prodded the Pentagon to field more of them, said Pentagon press secretary Geoff Morrell.

"He has gained an appreciation for what an incredibly effective war-fighting tool they are," Morrell said. "He has made it his personal mission to get the guys in the field as much of this capability as possible."

The Reaper, which flew its first mission Oct. 1, is the most lethal drone. It bristles with guided missiles and bombs similar to those aboard an F-16 jet. The Predator carries Hellfire missiles. Launched at airfields in Afghanistan, the Reaper is guided remotely by pilots in the U.S.

The Reaper travels about twice the speed of the Predator, increasing its value in the vast terrain of Afghanistan. Eventually, North said, he plans to use the bigger, faster drone in Iraq.

So far, the Reaper has attacked 16 targets in Afghanistan, North said, using 500-pound bombs and 110-pound Hellfire missiles.

"Unmanned vehicles present a whole new dimension to detecting and destroying of terrorists' cells," said Loren Thompson, a military analyst at the Lexington Institute. "It's almost like having your own little satellite over a terrorist cell."