The Soviet Union may join a proposed U.N. arms embargo against Iran, a top Defense Department official said yesterday.

Richard L. Armitage, assistant secretary of defense for international affairs, said Moscow's stance in the 7-year-old Iran-Iraq war will be a major topic at the Dec. 8-10 summit in Washington between President Reagan and Soviet leader Mikhail Gorbachev.

"I happen to believe that the Soviets eventually will be forced to join in an {arms} embargo," against Iran, Armitage told CNN.

"They're losing friends and influence in the gulf rapidly. . . . It's very difficult to force the Soviet Union, but I think events will lead them to believe that they have to come aboard," he said.

Moscow, one of the five permanent members of the U.N. Security Council, has objected to a U.S.-sponsored international arms embargo against Tehran.

Armitage said Moscow is the principal supplier of arms to Iraq, yet "the major foot-dragger on trying to bring the war to a close . . . and acting, as it were, in behalf of Iran."

Armitage was referring to reports that the Soviet Union is quietly cementing ties with Tehran to increase tensions between the United States and Iran so as to win a strategic edge in the Persian Gulf. U.S. warships are assigned to protect Kuwaiti tankers against Iranian attack in the gulf.