WASHINGTON — The number of times military fighters have been ordered to intercept planes straying into restricted airspace has declined by about 50 percent during the past two years.

Officials attribute the decline to tighter coordination among federal agencies and a growing awareness of flight restrictions among private and commercial pilots since the Sept. 11, 2001, terrorist attacks.

The Federal Aviation Administration and law enforcement agencies are getting better at identifying planes by checking records and flight plans before scrambling a fighter to get a closer look, said Air Force Col. John Zentner, operations officer for the North American Aerospace Defense Command, or NORAD.

Through mid-December, military fighter jets were dispatched 123 times in 2008 to intercept commercial or private planes that violated airspace restrictions, according to NORAD. That's down from 245 times in 2006.

Despite the decrease, civilian aircraft continue to regularly stray into restricted airspace, sometimes prompting fighter planes to intercept them.

The violations are an "an ongoing challenge for us," said Gen. Victor Renuart, commander of NORAD, which is responsible for protecting airspace over the United States and Canada.

There has never been an accident involving military fighters intercepting civilian aircraft. Still, having armed fighters flying near sometimes inexperienced pilots worries civilian aviators.

"Any time you have two aircraft operating in close proximity, the potential for an accident increases," said Chris Dancy, a spokesman for the Aircraft Owners and Pilots Association.

There were 338 violations involving pilots straying into restricted airspace in 2008 as of Dec. 17, according to NORAD. Most violators were private pilots. Not all the violations triggered an intercept. None of the aircraft posed a threat, NORAD said.

The military said it has strict procedures in place to avoid mistakes. A decision to fire on a civilian plane would have to be made by the defense secretary or designated military officials if he cannot be reached.

Their procedures are done at a safe distance so an inexperienced civilian pilot doesn't become alarmed.

Most civilian pilots quickly notice a fighter jet flying near them and follow instructions to divert or land at a nearby field. The pilot "realizes something is not right," Zentner said.

Fighter planes are generally sent up when officials are unable to make radio contact with an aircraft or it is not emitting signals from its transponder.