A heavily shrouded chapter of Cold War history has been reopened with new insights and controversy arising from recently declassified testimony of CIA chief Allen W. Dulles on spy plane operations against the Soviet Union in the 1950s and early 1960s.

Members of the U.S. intelligence community from the Dulles era were dismayed a week ago by news accounts about an allegedly undisclosed "CIA spy plane" shot down over the Soviet Union before the sensational U2 overflight of Francis Gary Powers May 1, 1960.

Dulles' testimony was given behind closed doors to the Senate Foreign Relations Committee May 31, 1960, during the international uproar about the U2 high-altitude reconnaissance jet plane and the collapse of the Paris summit conference in mid-May that year when Soviet Premier Nikita S. Khrushchev vented his outrage over the flight by the captured American pilot.

News reports last week based on Dulles' testimony said he disclosed that the United States lost "eight or nine" Central Intelligence Agency operatives on an earlier "spy plane" forced down in the Soviet Union.

State Department officials, after consulting with the CIA, told questioners that the reports were incorrect and that Dulles evidently was referring to the widely publicized loss of a U.S. Air Force plane and crew over the Turkish-Soviet border in 1958.

Many colleagues of Dulles similarly said he only was citing a known incident in 1958 -- a second one in which a plane was forced down across that frontier.

There were two problems with the explanations, however. The two groups were talking about different episodes, and neither fully meshed with Dulles' testimony. No one willing to speak about the affair can reconcile all of the discrepancies.

However, from information now available, it appears that in the tense U2 inquiry, Dulles deliberately scrambled his testimony to shield the identity of the then-supersecret National Security Agency, or unwittingly mixed up the two incidents. Possibly he did both.

As one associate recalled, a Dulles technique in maintaining an aura of certainty in his testimony was to "give quick answers to deflect questions and never appear hesitant or in doubt."

One encounter involved an Air Force C118 on a CIA courier mission with nine men aboard -- three formally assigned to the CIA -- and forced down about 100 miles inside Soviet Armenia in June, 1958. Five of the nine Air Force officers aboard descended by parachute, and four landed with the aircraft. All were released after 10 days of questioning.

In September, 1958, a second, deadlier incident occurred in the same region. An Air Force C130 with 17 military personnel aboard, on assignment to the National Security Agency, and packed with electronic eavesdropping gear for gathering intelligence, was shot down and crashed in Armenia.

Six bodies were returned by the Soviet Union, but 11 were never recovered. In 1962, after stormy dispute at the highest levels of the U.S. and Soviet governments, the 11 missing were officially "presumed dead," although efforts to recover the bodies were still being made in 1972.

That episode is recounted in a revealing book on the NSA, "The Puzzle Palace" by James Bamford. It reprints an extraordinary transcript of monitored conversations by Soviet fighter pilots during the attack on the C130. The transcript made public in 1959 by Secretary of State John Foster Dulles, Allen's brother, in an unusual effort to force the Kremlin to account for the missing crew members.

The United States never officially admitted that either plane was on anything but a normal Air Force mission. But the State Department virtually did that last week, perhaps inadvertently, when it connected the incident with Dulles' testimony.

Before and during the deep penetration of Soviet territory by high-flying U2 planes beginning in 1956, U.S. reconnaissance planes on ELINT (electronic intelligence) missions, known as "ferrets", operated around the vast periphery of the Soviet Union to pick up emissions of radar, ground communications and microwave signals.

Sometimes -- accidentally or deliberately -- they penetrated Soviet territory during what were called risky "fox and hounds" forays to set off Soviet air defense radar and in these instances American aircraft often were fired upon.

Allen Dulles, in his 1960 testimony, evidently overlapped both incidents. He said, "You may recall there have been several instances of planes that have strayed over Soviet territory which have been shot down. You recall the two incidents in Armenia and the Caucasus a few years ago, and there have been instances off the tip of Japan and some near Alaska."

He went on to say, "In one case we are still endeavoring to get back, you know--they haven't told us what happened to, I think, eight or nine of the crew of one of the planes that came down in the area of Caucasus."

"This was a civilian plane," Dulles said. "It was manned by employes of the Central Intelligence Agency, not by military personnel. They were in civilian clothes. It was an entirely civilian intelligence operation, and I was prepared to take the responsibility and document that responsibility."

Dulles' associates at the time included Richard M. Helms, later CIA director who was present in the U2 hearings to clear portions of the closed-door testimony for public use. Allen Dulles died in 1969.

Helms said last week that he has "no recollection at all" about that brief testimony but that "it is inconceivable" that there has been any third such incident involving loss of CIA lives withheld from the public or agency associates.

Similar comments came from other former Dulles colleagues, including Richard M. Bissell Jr., who planned the U2 program; Jack Maury, then-chief of Soviet operations; Laurence Houston, then-CIA general counsel; Ray S. Cline, former deputy director of CIA for intelligence, and Walter Pforzheimer, noted as a historian on intelligence, who last worked for the CIA in 1981.

Allen Dulles, these sources said, must have been referring to what they describe as the C118 "courier flight" forced down with nine Air Force men aboard in 1958. That flight would have had special memories for Dulles, for that aircraft was used regularly by Dulles or his deputy, Gen. C.P. Cabell, and that flight might have produced a sensational captive for the Soviets. Cabell had disembarked from it in Wiesbaden, West Germany.

The flight went on to a CIA base in Cyprus, then to a U2 base in Adana, Turkey, and was headed east toward Tehran when it crossed into Soviet air space and was attacked by Soviet MiGs. No plush, transport plane of that type, a modified DC6, CIA sources said, would have deliberately ventured into Soviet territory.

Five men bailed out immediately, with two reported burned as they escaped by parachute. They and the four who rode the plane to the ground were captured, and the Soviets evidently believed they had inadvertently crossed the border, CIA sources said, for they were "only lightly interrogated" and after 10 days of detention were released over the Soviet-Iranian border.

A far more dramatic and indignantly denied account about the incident has been given by L. Fletcher Prouty, a controversial writer on CIA history and for years a thorn in the agency's side. Prouty, a lieutenant colonel at the Pentagon in 1958, describes himself then as the liaison officer with the CIA and said he participated in the investigation of what he calls "a staggering goof" that caused consternation in the Eisenhower administration. Prouty's version is in his 1973 book, "The Secret Team: The CIA and Its Allies in Control of the United States and the World," and in subsequent magazine articles. Aboard the downed C118, he charges, there was "a highly classified briefcase" containing extensive information about CIA operations, plus "equipment for the then-supersecret U2 spy plane program." That information, Prouty claims, enabled the Soviets to shoot down Powers' U2 in 1960.

Prouty's claims were scoffed at last week by Helms, Bissell, Pforzheimer and others. Helms, who left the CIA as director in 1973, said, "I simply don't believe that Prouty is accurate. There is no substance to the charge."

Bissell said Prouty was not authorized for access to U2 information and said, "I don't see what information there could have been aboard that aircraft that could have helped the Russians" to bring down Powers' U2.

Pforzheimer has written that the Prouty book, despite the author's "considerable background and knowledge," was studded with "faulty recollections" and "unwarranted conclusions."

The CIA has declined official comment about any of these latest variations on this still-clouded chapter of U.S.-Soviet spy plane history.