U.S. Ambassador to the United Nations Andrew Young lost no time yesterday in advising Britain's new Conservative government against recognizing the recently elected Rhodesian administration of Bishop Abel Muzorewa.

Within hours of Conservative Party leader Margaret Thatcher's victory, Young said in a speech in Canberra, Australia, that recognition of the Muzorewa government would commit Britain to massive economic assistance and possibly military aid to Rhodesia.

Young told students and staff at the Australian National University that he thought Thatcher's government would not change the policy of her predecessor, James Callaghan.

"It's much different being in opposition than it is being a government," he said. "When you are in opposition all you have to do is oppose and you don't have to take the responsibility for your decisions."

In Lusaka, the Times of Zambia said the Conservative victory "could spell disaster" for southern Africa. The newspaper, owned by the ruling party, said Thatcher "is not sympathetic to the cause of the struggling masses of southern Africa."

President Carter said at a news conference in Des Moines, Iowa, that he had called Thatcher to assure her of his administration's support.

"We are convinced that the outcome of the election will not in any way interfere with the superb relations between our two countries," he said.

Speaking privately, administration officials conceded that they were "not all that happy" with the election results. The government ousted by Thatcher had worked closely with the Carter administration in a joint policy on Rhodesia.

Meanwhile, European conservative political leaders hailed Thatcher's victory as part of a conservative resurgence.

In Bonn, Christian Democrat leader Helmut Kohl said his party was heartened, adding that the election result could pave the way to more conservative leadership in the rest of Europe.