A U.S. pilot who mistakenly bombed Canadian troops in Afghanistan was under no threat of attack from small-arms fire before or after the 500-pound bomb was released, an Air Force commander testified at a military hearing today.

Lt. Col. Richard Anderson II, who was in charge of all coalition pilots' combat orders, said the pilot and his mission commander were also under "extremely tight" restrictions on weapons use. Standard procedure would have been to evade surface-to-air fire, not attack, he said.

Under cross-examination, however, Anderson indicated that he was unaware the pilot who dropped the bomb, Maj. Harry Schmidt, had been briefed that Taliban forces had rocket launchers powerful enough to put Schmidt's mission commander, Maj. William Umbach, in danger that night.

The defense has argued that Schmidt had good reason to believe he was under attack, because the gunfire he saw coming from the Canadians appeared to be aimed at Umbach's F-16.

The Air Force charged Schmidt and Umbach with involuntary manslaughter in the bombing last spring that killed four Canadian soldiers and wounded eight. The hearing, scheduled to end Jan. 24, is to decide whether the pilots should face a court-martial. If convicted, each faces as much as 64 years in military prison.

Lawyers for Schmidt and Umbach have said that the two were never told the Canadians would be performing live-ammunition exercises in the area. Defense lawyers indicated today that Schmidt mistook the Canadian groundfire for Taliban rocket launchers.

On a videotape taken from Schmidt's F-16, a flight controller can be heard saying "hold fire" after Schmidt requests permission to fire his 20mm cannons toward gunfire on the ground.

Anderson testified that Schmidt's request was unusual. "I really couldn't think of a tactical advantage" to using the cannons, he said.

Four seconds after the cannon request, Schmidt said he was "rolling in, in self-defense" to drop the guided bomb. Thirty-nine seconds later, the bomb was dropped, killing the Canadian infantrymen: Sgt. Marc Leger, Cpl. Ainsworth Dyer, Pvt. Richard Green and Pvt. Nathan Smith.

The deaths of the soldiers were the first for Canadian troops in a military combat operation since the Korean War.

Five Canadian survivors of the bombing testified earlier they were not firing into the air at the time of the bombing. They had been holding anti-tank exercises at Tarnak Farm, a firing range near Kandahar.

The defense lawyers have said the Air Force never passed along information about the allied exercises to pilots flying missions over the area.

However, Col. Lawrence Stutzriem, who was with the agency responsible for coalition air operations at the time of the bombing, testified that Air Force pilots flying missions in the area had received written orders warning that allied troops would intermittently use live ammunition.

The defense has also contended that Air Force-issued amphetamines taken by the pilots to prevent fatigue may have impaired their judgment. The Air Force says use of the pills is voluntary.