The crushing defeat of Prime Minister Indira Gandhi and her Congress Party in India is a major blow to Soviet policy in Asia, but the Kremlin is already moving to minimize the damage.

The Soviets' first assessment of the election, published today in Izvestia, the government newspaper, said Gandhi was beaten because of "mistakes and excesses" she committed after declaring a state of emergency in India in the summer of 1975.

Moscow previously had nothing but praise for Gandhi's tough measures. Soviet leader Leonid Brezhnev said during a visit here by the Indian prime minister last year that the measure had "full understanding of the U.S.S.R."

Under Indira Gandhi, Soviet-Indian relations flourished. The countries signed a friendship treaty in 1971 and a long-term accord on economic cooperation in 1973. The Kremlin regarded Gandhi as probably its best friend in the top councils of non-aligned states.

The Kremlin values its relationship with India so highly because of the role and influence that country has as a strategic counterweight in Asia to the Soviet Union's rival, China. Now the relationship will probably have to be reassessed.

The Soviets have generally described te victorious People's Party bloc as essentially rightist elements. They were extremely critical of all leading oppositionists when Gandhi declared the emergency. Western analysts said it was unlikely that the Soviets will be able to make the same kind of alliance with India's new leaders.

Nonetheless, Moscow's swift criticism of Gandhi - whose defeat Izvestia also blamed on her decision not ot cooperate with the Indian Communist Party in most states - shows that the Kremlin wants to waste no time in making amends the People's Party.

During the campaign, the Soviets had strongly supported Gandhi, speaking of her "imposing achievements," which invariably were contrasted with "the activities of those forces inside the country . . . that are opposed to India's line of strengthening political independence."

Her repudiation of the Communists, whose help she had accepted in the past, was not mentioned until now.