WASHINGTON — Piloted remotely from a Nevada air base half a world away or by soldiers on the scene, unmanned aircraft have become so indispensable in Iraq and in the war on terror that by next year the U.S. could be spending nearly seven times more on the vehicles than it did before the 9/11 attacks.

The drone aircraft, including the deadly Predators, were heavily used after February's bombing of a mosque in Samarra, Iraq, highlighting how prevalent they have become for a military thirsty for vehicles that can drop bombs or hover over targets without risking pilots' lives.

When Iraq erupted in ethnic violence after the Feb. 22 attack on the mosque, the planes — known as unmanned aerial vehicles, or UAVs — lingered over trouble spots so officials could use the crafts' video cameras to see where crowds were gathering and whether they were armed or violent.

Underscoring their importance, spending on the planes is expected to total at least $12 billion over the next five years. The spike in annual spending — from $300 million in 2001 to perhaps $2 billion next year — will pay for at least 132 UAVs, including a new version for the Navy, beefed up models for the Army and a major effort to solve technical problems.

"The services are demanding them — they can't get enough Predators in Iraq," said Dan Goure, defense analyst at the Lexington Institute. "Now the revolution has come. And it's going to be explosive over the next few years."

At least 700 unmanned aerial vehicles of all shapes and sizes are being used in Iraq, with dozens often jostling for room in the crowded airspace 24 hours a day.

The Army controls about 600 of them, mostly the smaller Ravens that soldiers can carry in backpacks and fling into the air for surveillance.

At least five times in December, the larger unmanned Air Force Predators — flown remotely by airmen sitting at consoles at a Nevada Air Force base — bombed insurgent strongholds in western Anbar province.

"The demand for a lot of these UAVs, especially the smaller ones, has gone through the roof," said Bruce Nelson, deputy director of the Air Force's intelligence, surveillance and reconnaissance programs.

Goure predicted spending in 2007 could reach $2.5 billion, though some of it will be hidden because it is classified or buried in other high-tech programs. The government buys many different unmanned systems for the military services, and the intelligence community also buys its own.

The Army's Raven weighs less than 5 pounds, can be carried in a backpack, and can be flung into the air to locate roadside bombs or beam back live pictures of targets.

Some of the smaller models cost as little as $25,000 apiece.

The Air Force's Predators, which can launch missiles, are 27 feet long and are flown remotely by airmen sitting far away in the United States.

And the larger Global Hawk surveillance aircraft, which can cost more than $80 million each, can reach an altitude of 65,000 feet and send back high-resolution imagery.