Two jets packed with military personnel pretending to be civilians took off from airports in the West on Tuesday in a twin hijacking drill designed to improve coordination among American and Canadian agencies.

About a dozen fighter jets from the North American Aerospace Defense Command scrambled to respond to the simulated hijackings, and ran through several scenarios.

"We're prepared to do it, trained to do it, and ready to do it, but we'd much rather it be the source of last resort," said Marine Maj. Mike Snyder, a NORAD spokesman. "But make no mistake we're ready to do it."

The scenario was planned before the Sept. 11 terrorist attacks, but Snyder said the events that day helped officials fine-tune the exercise.

The exercise, involving over 1,500 personnel from the United States and Canada, began at about 7 a.m.

One plane, a Delta Air Lines 757, took off from Salt Lake City and was headed to Elmendorf Air Force Base in Anchorage, Alaska. The other was a Navy C-9 airlifter, acting as another airliner. It traveled from Whidbey Island Naval Air Station at Oak Harbor, Wash., to Vancouver International Airport.

By mid-afternoon, the planes had landed and law enforcement officers on the ground began running through their own scenarios for dealing with the hijackers.

Snyder said the airborne portion of the scenario was a success but would not detail the specifics of the exercises. He hinted that the fighter pilots simulated shooting down the planes.

"For the exercise there was certainly a simulated response that might not be reflected in the aircraft landing," he said.

Such training exercises are held annually. Last year's exercise involved testing defenses against a cruise missile terrorist attack on the Florida Panhandle.

Since Sept. 11, NORAD has flown 22,000 sorties to watch the skies for hijackers and other threats, and fighter jets have responded more than 300 times when a plane raised suspicions — in many cases because the aircraft was off course or did not identify itself.

"NORAD is very well-trained and exercised regarding this particular scenario," Snyder said.

Among the agencies involved in Tuesday's one-day exercise were the FBI, the Royal Canadian Mounted Police, the new Transportation Security Administration, the Federal Emergency Management Agency and the Federal Aviation Administration.