Rhodesian prime Minister Ian Smith agreed yesterday to a U.S.-British call that Smith meet with his guerrilla foes in an effort to find a way to end Rhodesia's internal strife and bring about majority black rule.

At a State Department meeting, Smith and the three black leaders of his transitional government said they will take part in a peace conference involving all parties to the Rhodesia dispute, provided the conference is "well-prepared" and "without preconditions."

Their agreement presented U.S. and British policymakers with a victory and a potential problem in their efforts to find a solution to the conflicts between Rhodesia's ruling white minority and repressed black majority.

The action taken by Smith and his three colleagues yesterday marked their first unequivocal commitment to participate in the so-called all-parties conference - a plan that Washington and London have been pushing for more than a year.

By accepting, though Smith, in effect, put the United States and Britain in the position of having to win a similar, no-preconditions agreement from Joshua Nkomo and Robert Mugabe, leaders of the Patriotic Front guerilla forces fighting the Smith government from bases in neighboring Zambia and Mozambique.

In the past, Smith contended that nkomo and Mugabe, tacitly supported by Washington and London were laying down preconditions for a peace conference that would have given them control of Rhodesia.

Now, if the United States and britain are unable to coax the front leaders into a conference on the same terms accepted by the Smith government, the result is likely to be an upsurge of pressure in Congress for the Carter administration to abandon its efforts to include the guerrillas in a Rhodesia settlement and instead back Smith's go-it-alone plan for transition to black rule.

Senior State Department officials said yesterday they would approach the Patriotic Front leaders and the five black African "front-line states - Zambia, Angola, Botswana, Tanzania and Mozambique - supporting the guerillas in a bid to get the conference launched.

However, these officials noted that the effort has been complicated, at least for the moment, by the retaliatory raids the Smith government has mounted recently against guerilla bases in Zambia yesterday, Nkomo, citing the heavy death toll in the raids, bitterly rejected the idea of a peace conference and reiterated the guerillas' determination to gain power in Rhodesia through armed force.

The department officials, while saying that Nkomo's threats could not be treated lightly, also pointed out that the different factions in the Rhodesia dispute frequently have shifted their positions according to changing circumstances.

In the past, they noted, the United States has had a general impression that the front leaders would be willing to attend a conference; and they expressed guarded optimism about the prospects of getting them to the bargaining table.

In talking with reporters after yesterday's meeting, Smith and his colleagues said they had agreed to a five-point plan proposed by U.S. and British officials as a basis for discussion. The U.S. officials described the points as representing a summary and updating of the main elements in the year-old Anglo-American plan for Rhodesia.

The points listed are provision for free and fair elections open to Rhodesians of any color, arrangements for a cease-fire, formation of a transition administration to pave the way for majority rule, formation of armed forces to serve the resulting government, and agreement on the basic principles to be included in a new constitution, including guarantees of individual rights.

The U.S. officials took pains to stress that these are not preconditions but talking points for further negotiation and that neither the United States nor Britian has any preconceived ideas about how they should be worked into a final agreement.

In the past, for example, Smith has charged that the Anglo-American plan's call for changes in the Rhodesian armed forces meant that the white-controlled security forces loyal to his government would be dismantled and replaced by Nkomo's and Mugabe's men.

But, the U.S. officials said yesterday, Smith and his colleagues were assured that inclusion of the armed forces in the five discussion points means only that conference participants should address the problem and try to agree on what type of security force Rhodesia needs.

The breakthrough on the Smith government's acceptance of the conference came as Smith prepared to end his controversial 14-day visit to the United States and return to Rhodesia.

he and his three black partners - the Rev. Ndabaningi Sithole, Bishop Abel Muzorewa and Chief Jeremiah Chirau - came in hopes of swinging the Carter's administration's support behind Smith's "internal settlement" plan for a transition to black rule in the breakaway British colony.

Smith's plan calls for elections, with black participation, to produce a new government by the end of the year although Smith now says that technical difficulties may force postponement for several months.

However, the Carter administration, which has continued U.S. policy of regarding the Smith government as illegal, remained unconvinced. In a meeting last week with Secretary of State Gyrus R. Vance, Smith was told flatly that the United States does not believe there can be a successful Rhodesia solution without taking the guerillas into account.

Vance reiterated the U.S. and British call for negotiation with the front leaders. At the time, though, U.S. sources say, Smith refused to go any further than to say he would think it over.

Later, in a meeting with members of the Senate Foreign Relations Committee, Smith said he and his partners were willing to go to a conference without preconditions. That offer, relayed to the administration by the committee members, resulted in yesterday's agreement reached at a meeting with David Newsom, undersecretary of state for political affairs, and British Ambassador Peter Jay.