The Soviet government expressed guarded hopes today that President-elect Ronald Reagan would adopt a "constructive approach" that would lead to improved relations between the two countries.

The official Kremlin reaction came in the speech by new Premier Nikolai Tikhonov after President Leonid Brezhnev congratulated Reagan on his victory and voiced hope "that your activity in this high post will help improve" bilateral relations.

"We are coming out in favor of mutually advantageous cooperation with that biggest Western country for the sake of the Soviet and American peoples, for the sake of detente and the maintenance of peace," Tikhonov said in an address marking the 63rd anniversary of the Bolshevik Revolution.

But Tikhonov, in his first major pronouncement since he replaced the ailing Alexei Kosygin last month, also assailed the United States in what political observers saw as an indication that Moscow foresees tense relations with a Reagan administration.

"American imperialism and its accomplices," declared Tikhonov, "have taken the path of undermining detente, aggravating international tension, escalating the arms race, of adventurist actions [around] the world, a course of militant anti-Sovietism."

Implying that President Carter had failed to "display a high sense of responsibility" in bilateral matters that have "a big impact on the international situation as a whole," Tikhonov said, "in this context, one would like to express the hope that the new administration will display a constructive approach" to its relations with Moscow.

His speech, the traditional keynote address on the eve of the anniversary of the Bolshevik Revolution, was a restatement of Moscow's anger and ill feelings toward Washington that have emerged as the central bilateral theme during the last two years.

"Wherever a conflict arises, the United States seeks to aggravate it further," Tikhonov asserted. "Militaristic circles with cold cynicism draw up versions of nuclear war, each one more adventuristic than the last."

Although the Soviets want detente, Tikhonov asserted, "we of course cannot but draw the proper conclusions for ourselves from the intensification of trends in U.S. foreign policy."

Meanwhile, the tone of Brezhnev's congratulatory telegram to Reagan was far cooler than a similar telegram sent to Carter four years ago. Brezhnev expressed "the hope that your activity in this high post will help improve relations between our countries for the sake of the Soviet and American peoples and the consolidation of peace." Four years ago, the official message noted that both countries had made improvements in their relations.

Neither Brezhnev nor Tikhonov mentioned the pending SALT II treaty or other bilateral agreements. A five-year pact allowing the Soviets to buy a minimum 8 million tons of grain yearly from U.S. farmers expires next year, and there are no renewal talks under way.

Tikhonov staunchly repeated Soviet justification of its invasion of Afghanistan last December, accusing the United States, China, and Pakistan once again of trying to subvert the Marxist government of Kabul.

It was learned today that a number of Western ambassadors, including envoys from the United States, Canada, Britain, France, Italy, Belgium, will boycott the Red Square parade Friday as a sign of protest over the invasion of Afghanistan.