Britain plans a brief transitional period leading to legal independence for Zimbabwe-Rhodesia under which a British governor, backed by a limited number of military and police advisers, would restore London's control and supervise elections, British sources said today.

The proposals, disclosed to reporters, seem certain to draw sharp criticism from the Patriotic Front guerrillas just at a point when they seem on the verge of breaking the deadlock in the 37-day-old talks and rejoining the negotiations.

The leaders of black Africa's five "front-line" states tonight issued a conciliatory statement following an emergency summit in Tanzania on the deadlocked London conference. Speaking also for Zambia, Mozambique, Botswana and Angola, Tanzanian President Julius Nyerere said, "We are happy about the progress that has been made in London so far," according to Reuter.

Nyerere said that "there has been a hitch on the problem of land," a reference to the question of compensation for dispossessed white farmers. But, Nyerere added, "we are satisfied that the British understand the need for this clarification" demanded by Patriotic Front leaders.

["It is our hope now that the conference will move to the next crucial stage, which is the stage of agreeing about the implementaton of the constitution," Nyerere said.]

The British plan would, in effect, establish a thin veneer of British authority over the Salisbury government, leaving most institutions of the rebel government, including the military, basically intact.

It would remove Prime Minister Abel Muzorewa from power but leave most of his officials in positions of authority during what Britain hopes will be a brief transition period -- perhaps as short as three or four months.

The British advisers, who would include civil servants to take over some key ministries including defense and foreign affairs, would mainly be concerned with supervision of the election of a new government, the sources said. Under an agreement reached at the Commonwealth conference in Lusaka, Zambia, last August, officials from that organization would observe the election.

Muzorewa's Zimbabwe-Rhodesian administration would be left to run the day-to-day affairs of government, something the Patriotic Front is bound to protest.

The proposals differ markedly from ones presented by the Front last month. They portend a rocky future for the negotiations if guerrilla leaders Robert Mugabe and Joshua Nkomo accept a British-proposed constitution in order to join talks on implementing the charter.

Until now Britain has refrained from discussing and aspects of its position on the transition, saying that agreement had to be reached first on a constitution. The disclosures could be aimed at putting further pressure on the Front to accept the constitution so it can take part in the transition discussions.

The sources said the proposals represented tentative British thinking on the transition and that changes were still possible. For example, they said, it had not been decided yet whether the Parliament formed as a result of controversial elections in April would be dissolved.

It is likely that the proposals will be difficult to change during the negotiating procedure if Britain follows the same policy as it did during the talks on the constitution.

British Foreign Secretary Lord Carrington has maintained that there is little room for give because the British proposals attempt to come down in the middle between the warring government and Front and thus call for compromises from both sides.

Britain says it is seeking to gain a three-way agreement on a constitution and transitional arrangements leading to a new government that would then receive independence and international recognition and finally have the burden of economic sanctions removed.

Rhodesia, ruled by its white minority until installation of Muzorewa's limited black-majority government in June, has been an international pariah since it illegally declared independence in 1965 to retain white rule.

Britain has made it clear that the plan presented by the Patriotic Front last month was unacceptable although it did represent some movement from its previous stand that power had to be turned over to the guerrillas in any transitional arrangements.

The Front's plan calls for a British-chaired eight-member governing council with the guerrillas having four seats and the British and Muzorewa dividing the other four. Transitional commissions established by the council would control such key institutions as the military, police and civil service.