The Soviet Union celebrated its 63rd anniversary today with truculent words for the United States and a brief display of weaponry at a Red Square parade boycotted by more than a dozen Western ambassadors.

Defense Minister Dmitri Ustinov in a speech and an order read to all Soviet forces today declared the United States and "reactionary imperialist forces strive to bury detente, plunge mankind into a new cold war. The partnership of imperialism and Peking hegemonism is becoming increasingly dangerous to the cause of peace."

The two-hour traditional parade past the Kremlin was viewed by President Leonid Brezhnev and the other 13 Politburo members and assorted senior party officials. Ethiopian leader Mengistu Haile Mariam stood on Brezhnev's right atop the Lenin Mausoleum as more than 5,000 uniformed troops from various training and cadet units marched past. They were followed by a seven-minute parade of military equipment, including rocket-launchers, armored troop carriers, and T72 tanks.

The martial display was followed by brightly dressed gymnasts and tens of thousands of workers hauling floats proclaiming peaceful Soviet foreign policies, improved domestic production, and friendship for the oppressed.

In his order, made public by the Tass news agency today, Ustinov asserted that the new dangers posed by the Chinese and the West demand that party and state do "everything necessary for increasing the country's defense capacity. In single combat formation with the fraternal armies of the socialist community, Soviet armed forces vigilantly stand guard over the great revolutionary gains and are always ready to give a crushing rebuff to any aggressor."

U.S. Ambassador Thomas J. Watson Jr., as well as the envoys of Canada, Japan, China, and the NATO allies execpt Norway and Turkey, boycotted the parade in protest over the Soviet invasion of Afghanistan last December.

Revolution Day is traditionally a time for a tough defense speech. Last month, the party asserted it had in fact reduced the Soviet defense budget to just over 17 billion rubles ($24 billion at the official rate of exchange). Ustinov made no mention of this today, nor did he attempt to explain why the party would say it had reduced spending when dangers are said to be so high. Western analysts believe the Soviets spend about 15 percent of their national budget, or up to 115 billion rubles ($185 billion), on defense.

In his five-minute speech, Ustinov asserted that peace is opposed by "the forces of oppression, militarism and aggression, the actions of American imperialism and the aggressive NATO bloc."

Parade floats hailed Soviet-Afghan friendship, and the traditional parading of giant portraits of the leaders excluded one of Alexei Kosygin, the former premier. He resigned last month, but is not known to have been officially dropped from the Politburo.