In the judgment of President Reagan's departing chief adviser on the Soviet Union, Richard Pipes, if Bulgarian operatives were behind the attempt to assassinate Pope John Paul II last year, the chain of responsibility runs all the way up to Yuri V. Andropov, the new leader in the Kremlin.

"There is a big 'if' " in the linkage, however, Pipes emphasized after making his television interview assessment of Andropov's possible complicity in the shooting of the pope.

He said in the Cable News Network interview that any Bulgarian conspiracy to kill the pontiff would "certainly" have involved the Soviet KGB, and therefore "it could not have occurred without his Andropov's authorization." Andropov was head of the intelligence agency before succeeding Leonid I. Brezhnev as the Soviet leader.

Pipes stressed yesterday, after the interview was aired, that "the Bulgarian connection has not been solidly made -- and it is only inferential." On television he had said that "to me the evidence is very strong."

Furthermore, Pipes said, he was not basing his assessment on official intelligence reports but on press accounts of the investigation of the attack on the Polish-born pope in St. Peter's Square on May 13, 1981, and "a gut feeling of how these people operate."

Pipes also said, however, that "until the verdict is entirely in . . . it would be very risky for the president to come out and say anything charging the Bulgarians, let alone the Russians, with complicity."

Reagan himself said in a national radio interview yesterday, "I don't think I should express a belief on this. I'm just going to wait and see what the investigation brings."

Nevertheless, Pipes became the first prominent figure in the West to speculate publicly about Andropov's possible involvement. There also has been speculation among intelligence sources in Europe that Andropov's internal rivals, or external foes, may be spreading "disinformation" about "the Bulgarian connection" to undermine him.

The Soviet press agency, Tass, angrily denied any Soviet involvement in the attempt on the pope's life and assailed all charges of complicity by communist states as "absurd insinuations."

Pipes gave the television interview Friday on his last official day at the White House as director of East European and Soviet Affairs for the National Security Council staff. He is resuming his post as professor of Russian history at Harvard University, but is expected to continue as a consultant to the National Security Council.

Asked in an interview with The Washington Post how he would assess his impact on U.S.-Soviet policy during 22 months at the White House, Pipes said, "To the extent that it is possible for one staff member to have that influence I think I've had some influence, largely because of the way the president thinks, and my thinking happens to agree with his thinking."

Referring to his and the president's strong views about dealing firmly with the Soviet Union, he added, "The problem is that throughout the professional civil service, there are people who don't share this view. They'll conform, if they have to, but deep in their hearts they don't believe in it."

Pipes, 59, is no stranger to controversy. In 1976 he headed a "Team B" challenge inside the federal bureaucracy on intelligence estimates of Soviet military strength, which escalated the assessment of the Soviet threat.

When William P. Clark replaced Richard V. Allen last January as Reagan's national security adviser, Pipes and other members of the NSC staff gained greater access to the president and Pipes had an opportunity to brief him on occasion.

Pipes, although never a power in bureaucratic maneuvering, supplied academic reinforcement for Reagan's attitude toward the Soviet Union. As one colleague expressed it, "he gave intellectual credence to the visceral predilections of the California crowd."

Significantly, therefore, Pipes' views about the Soviet Union reflect the dominant perspective in the White House.

In the month since Andropov has been in power, Pipes said, "I don't see anything dramatic happening there at all." But it is inevitable, he said, that "the first concern of a new secretary general is with personalities, not with policies."

A new Soviet leader, Pipes said, "has to engage in the most vicious kind of bureaucratic in-fighting" and "it is hard to see how he can find the time to concentrate on grand strategy. He can do that only once he has consolidated his power. And that is still a long way off for this man.

"This regime," Pipes said, "has overwhelming internal problems. Above all, the status of the economy and the status of the empire."

Andropov faces a critical choice, Pipes said. Will the new leadership "take the road of reform, relaxation, and allow, both inside the Soviet Union and outside the Soviet Union, more freedom, more incentives, a more liberal model? Or will they try to revert to neo-Stalinism--more repressive? I don't venture to predict how this is going to turn out. It's an open choice."

A Soviet turn inward would neatly eliminate the United States' major problems with the Soviet Union.

"There is so much they have to do," said Pipes. "It is the only country in the world, so far as I know, where human life expectation is declining rather than rising. Over the past 15 years, the average life span of Russians has decreased from 66 to 62 years. Infant mortality is so high, they've stopped publishing statistics for years now.

"Isn't that absurd? That they are traveling in space, and their people on Earth are living worse and worse?" Pipes continued. "So essentially what we want them to do is to divert their energies internally . . . then the system begins to change inevitably, and they become less of a threat to us."

Pipes dismissed the notion that it is up to the United States "to take any first step, or that we are failing to respond to any gestures from Moscow," saying, "I don't see so far any gestures from Moscow."