WASHINGTON, March 9— Just three days after Cardinal Karol Wojtyla of Cracow became Pope John Paul II in 1978, the Central Intelligence Agency predicted that the installation of the first Polish pontiff would lead to political instability within Poland and the erosion of the Soviet Union's ability to control its Eastern European empire, according to newly declassified C.I.A. documents.

In the analysis, in October 1978, the C.I.A. forecast that Moscow would find it increasingly difficult to ''check and to counter Poland's instinctive, cultural and political gravitation to the West.'' In fact, the Solidarity movement, a Polish workers' rebellion against Communist rule that was supported by the pope, began just two years later, and ultimately played a crucial role in ending Soviet control over Eastern Europe.

Over the long run, the C.I.A. report predicted, ''the election of a Polish pope will contribute to an increase in nationalism in East Europe and will raise the consciousness of Orthodox churches and churchmen in the area.''

That report was among 19,000 pages of previously secret C.I.A. documents declassified and released today in conjunction with a conference at Princeton University on the history of the C.I.A.'s analysis of the Soviet Union. The 850 reports cover a broad range of military, political and economic topics from the early years of the cold war to the Soviet Union's demise in December 1991.

Some documents shed new light on how the agency viewed the Soviet Union during the final decade of the cold war, a period when political debates raged in the United States and elsewhere in the West about the nature and scale of the Soviet military threat.

Since the end of the cold war, the agency has been heavily criticized for failing to predict the Soviet Union's collapse, and for focusing too heavily on Moscow's military strengths without acknowledging how economic stagnation and changes in Soviet society were undermining Communist Party control.

But in fact, a recurring theme in the newly declassified reports from the late 1980's and from 1990 and 1991 was the notion that reforms by Mikhail S. Gorbachev, the Soviet leader, were imposing dramatic trade-offs between the military and consumer economies, and that something in the Soviet system would have to give.

By 1990, the C.I.A. believed it was probably already too late for Mr. Gorbachev's plans to succeed.

''Gorbachev's perestroika program is at a critical juncture,'' said a C.I.A. report in March 1990. ''He is preoccupied by the decline of the Communist party's authority, social unrest, secessionist movements in non-Russian republics and continued economic deterioration. These developments will come to a head this year and make it increasingly difficult for Mr. Gorbachev to continue his policy of managed democratization and market-ization.''

The report concluded that the social and political upheaval confronting Mr. Gorbachev's reforms ''are the direct result of Gorbachev's own policies.'' His initiatives have accelerated ''the disintegration of the old system's social control mechanisms -- thereby releasing powerful centrifugal forces that threaten the country's unity.''

The documents -- like other previously declassified reports -- show that the C.I.A. was increasingly skeptical that the Soviet Union could afford to keep up with the United States in the arms race, especially during the Reagan administration's military buildup.

A 1987 report on the Soviet response to President Ronald Reagan's Strategic Defense Initiative, for example, concluded that it would be extremely difficult for Moscow to keep up with an American ''Star Wars'' program. The Soviets would have to pour so much money into countermeasures or its version of missile defense that it would face extremely painful economic choices between its military budget and its consumer sector, this report said.

''Soviet statements indicate that Moscow believes that the cost of deploying advanced strategic defenses while modernizing and expanding offensive forces would be prohibitive,'' the report stated. ''Technological stagnation of their forces in the face of continually improving U.S. strategic defenses would upset the strategic balance and ultimately undermine their superpower status.''