The Air Force's U-2 and TR-1 spy planes were one of the gulf war's best-kept secrets: They began tracking Iraqi troops and equipment in August and are still in the region providing intelligence.

"I think they were extremely important," said an Air Force source, who spoke on the condition he not be identified.The U-2s and TR-1s were used extensively for everything from monitoring Iraqi equipment and troop concentrations to hunting Scud missiles and assessing the impact of allied bombs, the source said.

Yet, the single-engine planes, which can fly at altitudes above 70,000 feet, aren't mentioned in an Air Force white paper issued this month that described the performance of every other aircraft in the victory over Iraq.

The report says only that the large investments in intelligence to provide information for all coalition forces "were wise expenditures of taxpayer money."

A U.S. media pool that visited an air base in western Saudi Arabia during the 43-day conflict saw U-2s and TR-1s taking off and landing. But the reporters were barred by the military from even mentioning their presence in the gulf.

The Pentagon only reluctantly agreed to acknowledge their role now.

The Air Force source said publicizing the presence of the planes could have made it easier for the Iraqis to keep tabs on their takeoffs and landings and conceal equipment or operations the Americans wanted to observe.

The military also still appears sensitive to the international furor created in 1960 when the Soviets shot down a U-2 over Russia with a surface-to-air missile.

The incident, which exposed the CIA's spy flights over the Soviet Union, caused the collapse of a Big Four summit and cancellation of a visit to Moscow by President Dwight Eisenhower.

The U-2 pilot, Francis Gary Powers, spent 21 months in a Soviet prison before being exchanged in 1962 for master Soviet spy Col. Rudolph Abel, who had been arrested in New York. Powers was killed in a 1977 helicopter crash.

Asked whether the 1960 incident still colors the public perception of the plane, the Air Force source said, "Yes, I do - unfortunately."

Americans often ask if it's the one that was shot down, he said, and then they say, "You mean they're still flying?"

The U-2, with long, straight wings and gliderlike characteristics, made its debut in 1955 and has been used for worldwide strategic reconnaissance.

The TR-1, which uses the same basic air frame, was designed for NATO and flew its first mission in 1981. Its main job was to seek out targets and tell NATO fighter-bombers where to strike.

The U-2, modernized with a new engine and advanced avionics, is virtually the same as the TR-1 except for "minor, technical differences," the source said.