In a surprising reaction, Britain indicated today that it might be prepared to accept Prime Minister Ian Smith's own plan for a Rhodesian settlement based on the principle of one-man, one-vote.

British Foreign Secretary David Owen said it was still difficult to say whether the talks Smith is initiating next week with moderate black leaders living inside Rhodesia could lead to a satisfactory settlement of the 12-year-old dispute.

But he did not immediately rule out the possibility that the Smith plan might work despite the likelihood that black guerrilla forces based outside the country and fighting to topple the white minority government will be left out in the cold.

While black nationalist leaders living in Rhodesia generally praised Smith's plan, which the prime minister announced yesterday, those outside the country sharply condemned it.

Owen, in a statement issued in London, said that Britain's "fundamental principle is that independence (for Rhodesia under black rule) must involve a genuine transfer of power to a government representing the majority of the people of Rhodesia following elections on the basis of universal adult suffrage.

"The elections must be conducted in a manner which is demonstrably free and fair and all peoples and parties who intends to live in a future, Zimbabwe should be free to participate if [WORD ILLEGIBLE] Zimbabwe should be free to participate if they wish to do so whether they are at present living inside of outside Rhodesia." he said.

His statement seemed to imply that if Smith at least invites exiled nationalist leaders to participate in the elections. Britain would back an "internal solution," whether the exiles agreed to return or not.

In announcing his qualified acceptance of universal suffrage last night, Smith said he was acting on his own because the latest British-American peace plan for Rhodesia had failed. The plan, announced Sept. 1, called for Smith to surrender power and make way for British and United Nations-supervised elections for a black majority government.

Britain's unexpectedly soft reaction to the Smith announcement may reflect its loss at what else to do following its failure to get Smith and exiled black nationalist leaders of the guerrilla forces to acept the British-American plan.

In Washington, Tom Reston, deputy assistant secretary of state for public affairs, said the State Department considers the British-American plan still in effect. He said U.S. officials saw nothing in Owen's statement to indicate that Britain might be moving in a different direction than the United States in dealing with Smith.

In the past two years, the United States and Britain have stepped up their efforts to pressure Smith into accepting majority rule in Rhodesia, where blacks outnumber whites by 6.5 million to 270,000.

In 1965, Rhodesia, a British colony, unilaterally declared independence in a move designed to preserve local white rule. As recently as last year, Smith said publicly, "I do not believe in black majority rule - not in a thousand years."

Smith accepted a proposal by Henry A. Kissinger, then secretary of state, in Septemner 1976 that included majority rule within two years after formation of a half-black, half-white interim government. Smith pulled out of this agreement after leaders of the five black African front-line countries supporting the nationalists refused to accept the interim government provision.

This year the Carter administration, in one of its major foreign policy efforts, worked for several months with Britain to formulate the British-American plan, which called for transfer of power from the Smith government to Britain during a transition period that was to bring black majority rule by the end of 1978.

AT the topmost level of British foreign policy. Washington Post correspondent Bernard Nossiter reported from London, officials stressed that Smith's statement yesterday was a major change in the right direction. Owen is known to believe that Smith has now employed a new and rather better wording than ever before.

This has convinced experts in London that Owen and the Labor government are ready to junk a key element in the British-American plan - forming a new Rhodesian army in the future black-ruled state around the guerrilla forces run by the Patriotic Front of Joshua Nkomo and Robert Mugabe.

The five front-line black African states' leaders have strongly pressed for that element and their support, in turn, is regarded as crucial for war or peace since the guerrilla operate from bases in these five countries.

Top foreign policy makers in London, Nossiter repored, expect that the leaders of the five states - Zambia, Mozambique, Tanzania, Angola and Botswana - will denounce the Smith proposal because it appears to leave Nkomo and Mugabe and the guerrillas out in the cold.

The experts in London believe that Smith hopes his package will be attractive enough, however, that the guerrillas will drift away from the Patriotic Front, satisfied with some form of majority vote.

One caution raised by the British experts is that Smith may be attempting to preserve some form of white veto in any black-dominated legislature. In addition, they note that Smith, while not being explicit, tied law and order, which British experts interpret as a clear intention to keep control of Rhodesia's soldiers and police in white hands.

Rhodesia's black leaders differed sharply today in their reaction to Smith's announcement that he has accepted the one-man, one-vote principle white minority can be found and that he is planning to begin talks next week toward an internal solution.

Moderate living in Rhodesia hailed his statement as practically the end of their struggle to establish black majority rule. Radicals in exile warned that anyone dealing with Smith would be regarded as a "traitor" an "as much a target as the enemy."

Their contradictory statements made is clear as never before just how seriously fragmented the Rhodesian black nationalist movement presently is between those who have gone abroad to take up arms against the white minority government and those who have chosen to remain inside and fight it through peaceful means.

Observers here felt that in making his offer to accept universal adult sufferage, Smith was recognizing the mounting effectiveness of the guerrillas while seeking to circumvent them by dealing only with the moderate black leaders.

A spokesman for the internal African National Council faction led by the Rev. Ndabaningi Sithole said in Salisbury. "We think we have got what we have been fighting for." The traditional tribal leader, Chief Jeremiah Chirau, said, "An end to terrorism must be in sight because the fight for majority rule in Zimbabwe has been won."

Zimbabwe is the African nationalist name for Rhodesia.

Chirau called upon naionalist guerrillas fighting in the bush "to come home peacefully" because, he said, "majority rule is now definited so the need for fighting falls away."

There are an estimated 3,000 to 3,500 guerrillas now active inside Rhodesia and another 8,000 to 10,000 in training outside, most of them in Zambia, Mozambique and Tanzania but also some in Angola.

A spokesman for the Patriotic Front, the umbrella guerrilla organization as "political gimmicks." He said in Lusaka that the guerrillas were not fighting for one-man, one-vote but for the independence of the country from white rule and that the struggle would continue until Smith surrendered power to "the people of Zimbabwe."

He said that the internal black leaders would be branded as "traitors," adding "If they truck along with the enemy, then they are as much a target as the enemy."

The spokesman renewed the Front's appeal to Chirau, Sithole and Bishop Abel Muzorewa, leader of the United African National Council, the third internal faction, to join the guerilla movement, saying "There is still sufficient room for them inside the liberation forces,"

Informed observers here believe that although the South Africans have been nudging Smith to accept majority rule for over a year now, they want a settlement that will have international approval so that U. N. sanctions against Rhodesia can be lifted.

This is considered unlikely unless Smith's new initiative gets the cooperation of at least one of the two guerilla groups based outside Rhodesia.

South Africa also faces elections in five days and an indication of support for majority rule in Rhodesia likely to alienate a large section of the electorate.

"The government won't be eager to comment; it's in an embarrassing position," one observer said."They've been leaning on Smith but they don't want the voters here to know that."

South Africa has been cooperating with the Anglo-American initiative to bring about a solution to Rhodesia's constitutional crisis that would include both the inteternal and external Rhodesian nationalist factions.