As war refugees flooded South Korea's roads in 1950 and 1951, American jets attacked groups of Koreans in civilian clothes on suspicion that they harbored enemy infiltrators, according to declassified U.S. military documents and Korean and American witnesses.

Large numbers of South Korean refugees were killed in some cases, witnesses recalled. In one strike, U.S. firebombs killed about 300 civilians trapped in a cave, Korean survivors said.

After-mission reports from the Korean War show that Air Force pilots, flying in support of retreating U.S. troops in mid-1950, sometimes questioned their targets. In one, pilots said a Korean group that was strafed at an airborne controller's instruction "could have been refugees."

Some of those pilots, in recent interviews, said they worried at times that they were machine-gunning innocent people.

"We were concerned, very concerned," said Air Force retiree Herman Son of St. Louis. He said it "was by no means clear on the surface who these people were."

Some former pilots said they remember breaking off attacks when they realized their targets were civilians.

"Pilots have difficulty in determining whether personnel in enemy-held territory are noncombatants," reads an after-mission report by pilots in Son's 35th Fighter-Bomber Squadron.

The new information, on which the Pentagon had no direct comment, sheds light on yet another hidden side of the "forgotten war" of 1950-53, a conflict in which U.S. air power often proved pivotal. Associated Press articles in September and October cited U.S. veterans, Korean witnesses and declassified documents in reporting that hundreds of other South Korean refugees were killed by Army troops in mid-1950 as the retreating Americans struggled to defend South Korea against a North Korean invasion.

American ground commanders feared that enemy soldiers, disguised in the common white clothing of civilians, were joining South Korean refugee columns in order to penetrate U.S. lines. Documents found in declassified military archives show that some troops were ordered to shoot approaching civilians--orders that military law experts said were illegal.

"People in white" became Air Force targets as well, according to the once-secret Air Force files.

"Some people in white clothes were strafed three to four miles south of Yusong," an after-mission report by four 35th Squadron pilots noted on July 20, 1950. A spotter aircraft, or controller, ordered pilots "to fire on people in white clothes," the debriefing report said.

The Associated Press located the declassified debriefings at the U.S. Air Force Historical Research Agency at Maxwell Air Force Base, Ala., and at the National Archives in College Park.

Advised of the findings on the air war, chief Pentagon spokesman Kenneth Bacon reiterated that completing a probe into an earlier AP report on a large number of civilian deaths at No Gun Ri, South Korea, on July 26-28, 1950, is the first priority. "Then the department will decide if other incidents warrant further study," he said.

Since the report about No Gun Ri was published, the South Korean Defense Ministry has received petitions for investigation or compensation relating to at least 37 incidents in which U.S. forces allegedly killed South Korean civilians during the Korean War, the ministry said. Witnesses said they refrained from speaking out after the war because they feared reprisals from the South Korean military, which ruled the country until 1992.

Some of the reported U.S. air attacks on refugees occurred in January 1951, another period of retreat, when U.S. forces and South Korean refugees were driven deeper into South Korea by North Korea's Chinese allies, but American warplanes still monopolized the skies.

Villagers said American bombing and strafing killed about 300 South Korean civilians on Jan. 20, 1951, at a cave where they had taken refuge in Youngchoon, 90 miles southeast of Seoul, South Korea's capital.

An observer plane circled, and four planes dropped incendiary bombs near the cave's entrance, villagers said. Most victims were suffocated by smoke.

"People yelled and cried for their children," said Cho Bong Won, 64.

Earlier that week, 60 miles to the west, another 300 South Korean refugees were killed by a U.S. air attack as they jammed a storage house at the village of Doon-po, said survivor Kim In Tae, 58. Kim, a Presbyterian minister, said the planes dropped the bombs after the refugees had set a fire outside to keep warm.

The petition from Hong Won Ki, a retired newspaper executive, describes an air attack on Yong-in, 30 miles south of Seoul, after refugees rushed outside to wave at approaching U.S. planes, and a second strafing the next day, Jan. 12, 1951.

On Jan. 15, villagers said, planes returned. The villagers described strafings and apparent napalm attacks.

Other South Korean reports have surfaced about air attacks on civilians in July and August 1950, around the time of No Gun Ri, including attacks on a schoolhouse full of children and on refugees heading south near No Gun Ri a few days before the strafing and killings there.