Prime Minister Margaret Thatcher has received a report from a team of Conservative Party observers concluding that the Rhodesian election last month was sufficiently free and fair to satisfy British conditions for recognizing the biracial government of Prime Minister-elect Abel Muzorewa, it was learned today.

Thathcer's team of observers, headed by former colonial secretary Alan Lennox-Boyd, now Lord Boyd, reportedly also expressed reservations, however, about Rhodesia's new "internal settlement" constitution, which gives a disproportionately large share of power to the white minority.

Lord Boyd's report is expected to be used by Thatcher and her foreign secretary Lord Peter Carrington, in a cautious, slow-moving process to find a way to recognize the Murzorewa government and lift economic sanctions against Rhodesia without irreparably damaging Britain's relationships in the United Nations, its own Commonwealth of nations, and black Africa.

Carrington will conduct extensive international consultations on recognition of Rhodesia, beginning with a meeting here next week with U.S. Secretary of State Cyrus Vance. They are likely to continue through the Commonwealth meeting that Carrington, Thatcher and Queen Elizabeth II are to attend in Lusaka, Zambia, in August.

These consultations also will include talks with Bishop Muzorewa and other Rhodesian leaders, begun in Salisbury today by special British envoy Anthony Duff of the Foreign Office. The Thatcher government is expected by well-informed sources here to press Muzorewa to change the constitution to increase black participation in the government and make it more acceptable to world opinion.

This timetable is not expected to be alterd by the conclusions of the Boyd report, yesterday's U.S. Senate resolution calling on President Carter to end economic sanctions against Rhodesia, or the considerable pressure on Thatcher from within her own Conservative Party to move more quickly toward recognition and lifting sanctions.

The outgoing Labor government here, working with the Carter administration, had insisted that only internationally supervised elections with participation by the Patriotic Front guerrillas - who boycotted the internal settlement election - could bring an end to the Rhodesian civil war and produce an effective black-majority government.

Both Thatcher and Carrington made clear this week that the new Conservative government has decided that what it judged a freely and fairly elected black-majority government had made a major change in Rhodesia that necessitated a change in British policy.

"It is our objective," Thathcer said yesterday in outlining her government is policies to the House of Commons, "to build on that change to eventually return [Rhodesia] to legality in conditions which achieve wide international recognition." She added that "we must and we will take into account wider international implications."

It was a much more cautious statement of Thatcher's intentions on Rhodesia that her frequent campaign declarations that Britain must automatically recognize a freely and fairly elected black-majority government there under the internal settlement.

Thatcher apparently has been persuaded by Carrington, Foreign Office diplomats and others who warned that a precipitate move to recognize the Muzorewa government could harm Britain in its relations with the Carter administration, the United Nations, the Commonwealth and Britain's trading partners in black Africa. She was reminded that nothing need be done about economic sanctions against Rhodesia until they came up for renewal in Parliament in November.

This gives the Thatcher government time to lay the diplomatic groundwork for recognition and for removal of sanctions, to attempt to persuade Muzorewa to make his government more acceptable to world opinion, and to see whether Muzorewa's government survives.

Thatcher may now have more time on her side, if she can withstand the pressures from the right wing of her Conservative Party, than President Carter has in Washington.

Although the contents of the Boyd report may not be made public until after Carrington meets with Vance next week, sources familiar with the conclusions reached by Boyd's team of observers siad they were impressed with mechanics of the Rhodesian election and the participation by black Rhodesians given the right to vote for the first time.

This was the conclusion of other Conservative members of the House of Lords who observed the election on their own. Many Conservative politicians here have long sympathized with the ruling white minorities in Rhodesia and South Africa and believe that the threat of Soviet influence in Africa is a much more pressing problem that eventual black sharing of power in southern Africa.

The lone dissenter thus far among British peers who observed the Rhodesia election is a former leading Liberal politician, Lord Chitnis, who issued a report today on behalf of an adhoc parliamentary civil rights group, calling the election "a gigantic confidence trick."

Chitnis said black Rhodesians were frightened into voting by the government and their white employers, often did not know that they were voting for, and never had the opportunity to vote yes or no on the internal settlement and constitution.