LAKE FOREST, Calif. —

In 1980, Abraham Karem, an engineer who had emigrated from Israel, retreated into his three-car garage in Hacienda Heights outside Los Angeles and, to the bemusement of his tolerant wife, began to build an aircraft.

The work eventually spilled into the guest room, and when Karem finished more than a year later, he wheeled into his driveway an odd, cigar-shaped craft that was destined to change the way the United States wages war.

The Albatross, as it was called, was transported to the Dugway Proving Ground in Utah, where it demonstrated the ability to stay aloft safely for up to 56 hours — a very, very long time in what was then the crash-prone world of drones.

Three iterations and more than a decade of development later, Karem's modest-looking drone became the Predator, the lethal, remotely piloted machine that can circle above the enemy for nearly a day before controllers thousands of miles away in the southwestern United States launch Hellfire missiles toward targets they are watching on video screens.

The emergence of hunter-killer and surveillance drones as revolutionary new weapons in the wars in Iraq and Afghanistan, and in counterterrorism operations in places such as Pakistan and Yemen, has spawned a multibillion-dollar industry, much of it centered in Southern California, once the engine of Cold War military aviation.

Over the next 10 years, the Pentagon plans to purchase more than 700 medium- and large-size drones at a cost of nearly $37 billion, according to a Congressional Budget Office study. Thousands more minidrones will be fitted in the backpacks of soldiers so they can hand-launch them in minutes to look over the next hill or divebomb opposing forces.

This booming sector has its roots in the often unsung persistence of engineering dreamers who worked on the technology of unmanned aviation when the military establishment and most major defense contractors had little or no interest in it. Innovators such as Karem were often sustained by grants from the Defense Advanced Research Projects Agency (DARPA) and a handful of early believers, including the CIA.

Karem said he imagined his drones involved in a "tactical conflict with the Warsaw Pact, be it on the plains of Germany or as part of our Navy and Marines." He had to sell his company, and with it the prototype of the Predator, long before it became the icon of a new kind of warfare.

"I did not envision the collapse of the Soviet Union and the rise of warfare with nonstate adversaries," said Karem, an aeronautical engineer who served for nine years in the Israeli air force before settling in the United States in 1977.

The military had less than 200 drones the day before the attacks of Sept. 11, 2001; today it has more than 7,000, including minidrones.

Before Sept. 11, drones weren't "on the road map," said Tim Conver, chairman and chief executive of AeroVironment, which builds close-in surveillance drones for the military. Since the invasion of Afghanistan, the company has sold the military thousands of small drones.

The technology is significantly cheaper than traditional aircraft, and its potential uses increase as the craft become faster and stealthier.

Teal Group, a Fairfax, Va., market-analysis firm, estimates that nearly $100 billion will be spent globally on drones between now and 2019.

"Worldwide you have very limited adoption of UAVs [unmanned aerial vehicles], but foreign militaries have seen the success in Iraq and Afghanistan, and they want them," said Phil Finnegan, Teal Group's director of corporate analysis. The rise of drones has been a small boon for Southern California, where the aerospace industry has contracted painfully in the past two decades. About 10,000 state residents are directly employed in the drone sector. And for national-security reasons, much of the supply chain is kept onshore, generating jobs among contractors and subcontractors.

General Atomics Aeronautical Systems, which makes the Predator and the next-generation Reaper drone, is in Poway, north of San Diego. AeroVironment, which makes an array of backpackable minidrones, such as the Raven and the Wasp, is in Simi Valley.

Northrop Grumman is testing the X-47B, a carrier-based fighter drone, for the Navy in Palmdale. The RQ-170, the stealth drone manufactured by Lockheed Martin and used by the military and the CIA, is believed to have emerged from the company's classified facility, the Skunk Works, also in Palmdale, near Edwards Air Force Base.

In 1987, AeroVironment flew the first backpack-portable unmanned military aircraft, a nine-pound plane with a camera in its nose. It was called the Pointer.

When the first Special Operations teams went into Afghanistan in October 2001, they brought with them two Pointer systems that they used for low-altitude surveillance. Soon, word was going up the chain that the troops wanted more Pointers for Afghanistan's difficult terrain. High above them, the Predator and Global Hawk were also proving themselves.

"The Predator is my most capable sensor in hunting down and killing al-Qaida and Taliban leadership and is proving absolutely critical to our fight," Gen. Tommy Franks wrote in a 2003 Air Force background paper.