Secretary of State Cyrus Vance said here yesterday "it is a possibility" that the Soviet Union is behind the Hanoi government's effort to export Vietnamese refugees.

Vance was questioned about the refugee problem at a press conference at which Australian Prime Minister Malcolm Fraser made even stronger references to the possibility of Soviet involvement.

Fraser said that British Prime Minister Margaret Thatcher had spoken about the refugees with Soviet officials, including the Premier Alexei Kosygin, two weeks ago on the way to the Tokyo summit.

"In short, she got a raspberry," Fraser said. "She was told they were all drug addicts, criminals and subversives, and that it was an internal matter for Vietnam."

"Plainly, the Soviet Union would be in a position to influence the Vietnam government," Fraser said. "But if it has used its influence, it has not been to diminish the human trade.

"We have to keep in mind that Vietnam having embarked on this policy, that it could be a deliberate decision on the part of the Soviet Union to encourage it, to destabilize Southeast Asia and to destroy much of the benefit of the economic progress of the last 10 years."

While Vance said that Soviet involvement was possible, he added: "We do not know whether this is the fact."

Vance, Fraser and New Zealand officials discussed the refugee problem during the 27th council meeting of the ANZUS Alliance powers.

Vance also said it was possible that the United States might have to expand its naval patrols in the Indian Ocean - an area over which Fraser often accuses the Soviet Union of attempting to destablize.

In New Delhi, Foreign Minister Atal Bihari Vajpayee said that India was opposed to any strengthening of the U.S. naval presence in the Indian Ocean because it would invite a "corresponding increase of Soviet navy."

Meanwhile, government spokesmen for Thailand, Malaysia and Indonesia said their countries would try to keep out any more Indochinese refugees. A U.S. spokesman said earlier this week that Vance had received provisional commitments from those nations - plus the Philippines and Singapore - to continue accepting refugees pending a speedup of resettlement.