Defense Secretary Caspar W. Weinberger called yesterday for "reductions" in the number of Soviet representatives permitted to live in the United States, asserting that Moscow sends only people who are trained to hunt for U.S. military secrets.

Weinberger told a news conference that such reductions would be one way of blunting the carefully orchestrated Soviet campaign to acquire Western technology that was divulged in an intelligence report Wednesday.

U.S. intelligence experts, meanwhile, said that the report's unusually detailed findings represent a major breakthrough for the West in understanding the type of technology that the Soviets most need, their methods for acquiring it and the advanced Western equipment they have managed to obtain and copy. One intelligence source described the findings as a "windfall," alerting the United States and its allies where to focus their counterintelligence efforts.

Much of the information in the report came from rare Soviet defense industry documents passed to the French by a KGB agent who has since disappeared in the Soviet Union and is presumed dead, according to an intelligence source.

Other significant data was obtained from the former deputy director of the Romanian intelligence service, Ion Mihai Pacepa, who defected to the United States in 1978, and from FBI investigations of two Americans convicted in recent years of selling U.S. defense contractor secrets to Poland, the source said.

The report discloses the intricate workings of the Soviets' Military Industrial Commission, which directs thousands of Soviet and East European agents who hunt for military secrets by hiring Western smugglers and targeting U.S. universities, defense contractors, government agencies and scientific conferences.

An elite cadre of 300 "Line X" agents directed by the commission and 1,500 military intelligence officers operates abroad under the cover of science and commercial branches of Soviet embassies, Soviet trade missions and such organizations as the Soviet airline, Aeroflot, the report said.

Weinberger, alleging that the large number of Soviet representatives in the United States "widens the availability and possibility" of technology leaks, suggested that they be limited to the number of Americans living in the Soviet Union.

"We have to bear in mind, and it's only prudent to do so, that the Soviets don't send people to countries like the United States unless they are fully equipped, fully trained and they're part of the KGB," he said. "We have to understand how damage can be done by the gathering of this material set forth in that report."

Weinberger did not say if he would achieve the reductions by attrition or expulsion.

According to the State Department, 980 Soviets live in the United States, including embassy and consulate officials, journalists and U.N. and commercial representatives. There are 276 U.S. Embassy officials, journalists and businessmen in the Soviet Union.

The report said the Soviet technology-gathering apparatus increasingly relies on East European agents, who arouse less suspicion among Americans, to tap U.S. government agencies and universities for unclassified documents.