Conservative Party leaders today outlined a "fresh approach" that a Tory government would take on the racial conflicts in southern Africa, differing significantly from the present joint U.S.-British policy there.

Conservative leader Margaret Thatcher and her foreign policy spokesman, Francis Pym, outlined a strategy that would include:

Removing economic sanctions against Rhodesia and recognizing the legality of its new racially mixed government if the election there "takes place in reasonably free and fair conditions and with a reasonable turnout."

Ruling out the possibility of ever imposing economic sanctions on South Africa and instead trying less drastic means of persuading it to modify or end apartheid.

Urging the United States, other Western countries and the United Nations to stop favoring the black nationalist guerrilla movement in negotiations with South Africa over independence for neighboring Namibia.

Developing with the United States, the European Economic Community and friendly African nations "a new concerted policy" of using Western trade and economic assistance to "give the strongest encouragement and support to democratic solutions to African problems" and stop the spread of communism there.

Thatcher formally announced the Rhodesian and South African policies in a press conference and party manifesto that officially launched the Conservatives' campaign for the May 3 national election here.

Pym, who is a leading candidate to become foreign minister if the Conservatives win, supplied details in meetings with reporters today and in an important speech on Africa earlier this week.

Pym was noticeably critical of how the United States and the Labor government in Britain had reacted to developments in southern Africa in the last 18 months, when, he said, "the situation has gotten worse" because of diplomatic failures."

Pym said the Labor government and the United States made a "diplomatic error" by "prejudging" the election already begun in Rhodesia when they refused to send observers and ruled out the possibility of recognizing the legitimacy of the 'black majority government" being elected by "universal suffrage."

The Conservatives have sent six observers.

The U.S. and British governments had insisted on a U.N. supervised election that would be accepted by all parties, including the Patriotic Front guerrilla alliance of Joshua Nkomo and Robert Mugabe operating from outside Rhodesia. Nkomo and Mugabe are boycotting the election set up under the "internal settlement" negotiated by Prime Minister Ian Smith, a white, and black leaders inside the country.

Outgoing British Foreign Minister David Owen reiterated two weeks ago the Labor Party position that the internal settlement "virtually assures whtie domination of the key power centers in Rhodesia for many years to come" through disproportionate representation in the biracial government now being elected and continuing control of key postions in the military, civil service and courts.

he election, Pym said today, is "being held under very difficult circumstances because Britain, the United States and other countries did nothing to restrain the guerrillas from disrupting it." Nevertheless, he said, the election "could be a very important step on the road to an independent, free Zimbabwe-Rhodesia."

The Conservatives have the same objective as the United States, Pym said, "bringing peace to southern Africa. The argument is about how you get there."

In his speech earlier this week, Pym accused the Western countries, including Britain and the United States, of negotiating a plan for the independence of Namibia of allowing the guerrillas there to "countinue to pursue the path of violence" while negotiations continued.

Whatever happens in Namibia or with apartheid inside South Africa, Pym and Thatcher emphasized in the manifesto, the Conservatives 'are completely opposed to the imposition of economic sanctions on South Africa." They said sanctions would be ineffective, would hurt blacks in South Africa and neighboring nations the most and would damage western business and other interests.

All this, Pym said, "would give comfort only to the communists and those who seek a violent solution to the problems of southern Africa."

Pym and Thatcher contended that the most important problem in Africa is the threat of communism and the "substantial footholds" the Soviet Union and Cuba have established there. "The communist threat has never loomed larger," Pym said.

Although Pym and Thatcher both said today that they supported U.S. efforts to reach a new strategic arms limitation treaty with the Soviet Union, the Conservative manifesto warned that "the SALT discussions increase the importance of ensuring the continuing effectiveness of Britain's nuclear deterrent."

Asked about that, Pym said a Conservative government would still count on U.S. protection if Britain were threatened. "We have confidence in the United States," he said. "We both must work closely together."

Pym also said that Thatcher's lack of government experience in foreign affairs was offset by many trips she had taken to America, the Middle East and the Far East and the many heads of state she has met both here and abroad since becoming party leader.