The Blessing of the Bikes has been an annual curse for Southern Maryland law enforcement.

Nearly 100 officers in Calvert County took to the streets in May 2003 when Hells Angels squared off with Iron Horsemen. The year before, rifle-wielding officers perched on the rooftops of businesses to keep the peace.

This spring in nearby Charles County, officers tested a new instrument of vigilance: the CyberBug.

The three-pound surveillance drone -- borne aloft on a white, triangular wing and flown under joystick control -- fed streaming video of the bikers' movements back to officers on the ground. The Charles County Sheriff's Office hasn't purchased one of the $8,500 drones, but Capt. Michael Wyant said he sees possible applications: hovering over the woods to search for a missing child or probing a chemical or biological attack.

"It's certainly something of great interest to us," Wyant said. "It's real cutting-edge right now."

The CyberBug, made by Florida-based Cyber Defense Systems Inc., was just one of dozens of drones on display yesterday at the third unmanned aerial vehicle air show at Webster Field, an annex of Patuxent River Naval Air Station in St. Mary's County.

In Iraq and Afghanistan, the military has come to rely on unmanned aircraft for surveillance and attack missions, using everything from tiny craft that fit in a backpack to multimillion-dollar planes that can fly at 65,000 feet.

Drones also have a growing number of civilian uses, such as searching for schools of tuna, guarding borders and watching for forest fires.

Nearly 5,000 people, including Secretary of the Army Francis J. Harvey and U.S. Rep. Steny H. Hoyer (D-Md.), turned out despite the early morning drizzle to peruse the latest technology in rows of white tents and to watch flying demonstrations once the weather cleared.

"We like to say UAVs are designed to do the dull, dirty and dangerous work," said Robert Kornegay of Boeing, who is working on the development of the X-45, a stealthy, batlike drone with a 49-foot wingspan that can drop 2,000-pound bombs and is expected to be in use by 2007.

About 20 types of drones have flown thousands of hours of reconnaissance in the Middle East. The Defense Department has spent $1 billion since 2000 to research aerial drones, said Deputy Assistant Secretary of Defense Thomas J. Kuster.

"They offer to terrorists neither a high-value target nor a potential captive," he said.

In the United States, the Department of Homeland Security uses drones to watch for people crossing the Mexican border, Kuster said. The Army uses four types of drone: the Raven, the Shadow, the Hunter and the not-to-be-ignored Improved Gnat.

The Coast Guard is building a national security cutter that will have two vertical-launch drones that will be able to provide 16 straight hours of surveillance, said Coast Guard Rear Adm. Patrick M. Stillman.

In his view, drones would be useful for enforcing fishing regulations in Alaska or looking for drug traffickers in the Caribbean.

"The real face of transformation," he said, pointing to the airfield where the drones were zipping about, "is right here."

Under the NASA tent, scientists showed off the latest in drone research. Michael J. Logan of NASA displayed the "black diamond," which looks like a flying seat cushion and is piloted by someone wearing virtual-reality glasses.

"You're flying the bird as though you're sitting in the cockpit," said Logan, head of Small Unmanned Aerial Vehicle Laboratory at NASA's Langley Research Center in Hampton, Va. He says it might be used to help farmers find spots in their fields that need more water or fertilizer.

And what aerodynamic insight inspired the square shape?

"It fits in a box," he said.

Using drones for law enforcement bumps up against some obstacles, Wyant said: the cost, the need to train officers and problems of flying them in all types of weather. But the technology is attractive for being able to fly low and into potentially dangerous situations.

"At this point it's in research and development stage," he said. "We're just exploring."

Arie Arielly launches an electric Skylark, by EFW Inc., at the aerial drone show at Webster Field in St. Mary's.

At the air show for aerial drones, John Gardner, right, prepares wireless controls for the Raven, produced by AeroVironment Inc.