At 3:30 a.m. Washington time on May 1, 1960, senior CIA officials in the agency's operations center got a piece of information that greatly disturbed them: Soviet radars following an American U-2 spy plane suddenly stopped tracking the flight.

They did not know for sure, but the Soviet decision to discontinue tracking the plane flown by Francis Gary Powers was a strong indicator that it had been shot down. Shocked officials who had seen the Soviets try and fail time and again to down the high-flying spy planes, hastily began preparing their cover stories.A newly declassified CIA study on the U-2 program was unveiled Thursday at a reunion of the pilots, engineers and CIA analysts who built and ran a plane that began its career in the early years of the Cold War and remains one of the busiest in the U.S. arsenal today.

While generally enthusiastic about the U-2 program, the 1992 study, originally classified secret, gives an unvarnished account of the miscalculations that led to the Powers downing, one of the most embarrassing moments of the Cold War for the United States.

"After almost four years of successful U-2 missions," the developers of the U-2 program "became overconfident and were not prepared for the `worst case' scenario that actually occurred in May 1960," the report concludes.

Still, the problems and risks of the program paled in comparison to its successes, U-2 veterans said.

"We desperately needed to know what Soviet intentions and capabilities were," said CIA Director George Tenet. "In short, we were blind."

The photographs brought home on 300-pound film reels spooled in the belly of the aircraft provided war planners with military targets where they had had none; they enabled intelligence analysts to debunk Soviet claims of massive superiority in bombers and later missiles; and when crises broke out in the Mideast, the U-2 gave the White House a direct information source unfiltered by allied biases.

Carmine Vito, the first and only spy plane pilot to fly over Moscow and live to tell about it, remembers being more apprehensive than scared about the U-2 missions. Fear he saved for combat missions, which he had flown over Korea and would fly again over Southeast Asia.

"In Korea you were expendable. They wanted you to hit the target and if you didn't come home, well, that was too bad," Vito said. Reconnaissance missions were designed with survival in mind - so that pilots could return with their precious cargo of film.

The 333-page declassified study tells of then-CIA Director Allen Dulles' reaction on July 5, 1956, hours after Vito's flight, when his reconnaissance chief, Richard Bis-sell, told him what routes the U-2s had flown.

"Do you think that was wise the first time?"

"Allen," Bissell replied, "the first is the safest."

Despite early successes, President Dwight Eisenhower was telling Dulles he had "lost enthusiasm" for the Soviet overflights and warned that if the world found out, "the reaction would be drastic."

Pressed by his military chiefs, who were trying to develop a detailed target list in case of nuclear war, Eisenhower reluctantly allowed the flights to continue.