The Soviet Union's Communist Party leadership pledged itself today to significant changes in the economic policies it has imposed on the country in the past three decades in a bid to "radically" overhaul Soviet productive capability and achieve more autonomy in the management of Soviet industry by the end of the century.

In releasing major portions of a revision of the basic party program last rewritten in 1961, the party gave the most comprehensive view yet of new Soviet leader Mikhail Gorbachev's blueprint for the course of economic and social development in the country he is positioning himself to lead into the next generation.

The program, which will be discussed by local and regional Communist committees across the country during the next four months before being passed by the Central Committee at the party's 27th congress in February, explicitly criticizes the economic policies followed by the governments of the late Leonid Brezhnev and his predecessors.

It contends that military and strategic parity with the United States have been achieved, terming this "a historic accomplishment of socialism." While sharply critical of the United States on several specific points, the new program commits the party to seeking "fruitful and mutually beneficial Soviet-American cooperation in various fields."

It tones down some of the sharpest criticisms of the United States contained in the 1961 document. "Differences between social systems and ideologies are no reason for strain in relations," the program released today asserts.

The overall thrust of the document is to scale down the party's stated aspirations for achieving communism in its purest theoretical form, and to admit that the advance of humanity toward communism and socialism is uneven, shaky and controversial.

The program revises the omnibus promises and the hope of achieving communism in 20 years, emphasizing instead the development of "integral socialism," a new state in Soviet society. Socialism and communism are two consecutive phases of communist formation, it says, adding that "there is no sharp dividing line between them."

Since 1961, the revision says, analyses of domestic and international changes "offer an opportunity to define more correctly the perspectives for Soviet society's development."

The program reaffirms the party's goal of doubling and "radically" renewing Soviet production by 2000 and for the first time outlines the strategy for achieving it. It calls for coupling refinements in the Kremlin's central planning with greater autonomy in production enterprises and combining increased industrial investment with greater emphasis on "creative initiative of working people."

The program is laced with the language Gorbachev has used since he came to power in March to stress the need for economic improvements.

In economic and political terms it proposes a modernization in the means by which the party achieves the goals of communist society. It calls for more robotization and computerization in industry, and for the party to use contemporary tools such as public opinion assessments and television to maintain contact with the Soviet people.

Soviet and western analysts here view the revised program as a broad-based criticism of Nikita Khrushchev, who led the Kremlin when the original program was drafted and whose fallen career is associated with exaggerated predictions that communism would "bury" capitalism by 1980. The party "does not set itself the aim of foreseeing in detail the features of full communism," the new program says.

It attacks Joseph Stalin's "cult of personality" and Brezhnev's economic policies without naming the two. It says that "in the 1970s and early 1980s there were certain unfavorable trends and difficulties . . . due in considerable measure to failure to assess in due time and proper manner alterations in the economic situation and the need for profound change in all spheres of life, and failure to properly persist in making such change."

The program offers a bleak assessment of the future of capitalism, saying the "general crisis of capitalism is deepening."

It blasts the United States as "the citadel of international reaction" but it also calls for "normal and stable" relations between the superpowers.

The establishment of military and stategic parity between the Soviet Union and the United States, and between the Warsaw and NATO pacts, marks "a historic accomplishment of socialism," the program says, in a sweeping endorsement of the Soviet military achievement since the original party program was passed on the eve of the Cuban missile crisis.

But the revised program is viewed by analysts here more as the Soviet Communist Party's future road map than as a checklist of its accomplishments.

It provides the most detailed definition of the long-term plans for economic reform since Gorbachev began pushing for broad changes in the Soviet economy last spring. It proposes a "sharp turn toward intensification" and underlines the need for "serious structural changes" in the economy.

It sees as "vital further development and improvement in the effectiveness of cost accounting." It says that "the system of levers and incentives should effectively give advantages to the labor collectives that score successes in accelerating scientific and technical progress, put out better products and enhance the profitability of production."

In an unusual calling of attention to the influential Soviet intelligentsia, the program recognizes that "the number of intellectuals is growing and their creative contribution to material production and other spheres of public life is increasing."

Some Soviet analysts interpreted that as an indication of new-found concern for deepening the influence of the party in Soviet society.