Britain and the warring factions in Zimbabwe-Rhodesia agreed today on nearly all points of a plan to bring the southern African breakaway colony to legal independence under black-majority rule.

The few remaining differences are likely to be resolved Thursday, according to British sources, and the 10-week-old peace conference here will then move on to negotiation of a cease-fire, the last issue to settle in reaching a final peace agreement ending the 14-year conflict.

"We seem now to have got an understanding on all those issues that were sticky," said Joshua Nkomo, co-leader of the Patriotic Front guerrillas.

His optimism was echoed by the British and by other Patriotic Front sources. Front spokesmen also emphasized that there was no disagreement between Nkomo and Robert Mugabe, the other Front leader, as has been rumored here this week.

The British sources reiterated that the other party to the talks, the present black-majority government of Prime Minister Abel Muzorewa in Salisbury, has already agreed to the plan. The Patriotic Front is fighting the Muzorewa government, saying it is dominated by the white minority.

Both the British and the Patriotic Front made concessions in nearly eight hours of intensive negotiations yesterday and today on the British plan for holding new elections in Zimbabwe-Rhodesia during a transition period under a reestablished British rule.

Under pressure from the conference chairman, British Foreign Secretary Lord Carrington, the Patriotic Front agreed to a transition period of less than six months, dropped a demand to share power with the British governor during the transition, and agreed to other British proposals on the conduct of the election.

Under the urging of President Kenneth Kaunda of Zambia, who met with Carrington and Prime Minister Margaret Thatcher here last weekend, the British agreed to give the Patriotic Front military forces equal status with the troops of the Salisbury government by placing commanders of both sides on a cease-fire commission reporting to the governor. The British would provide food and housing for the Front guerrillas.

The British and the Front also moved toward agreement to have troops from Britain and other Commonwealth countries monitor a cease-fire. The British agreed to move -- with the help of other nations, including the United States -- the Front guerrillas and other refugees from Zambia and other neighboring African countries back into Zimbabwe-Rhodesia for the new election and resettlement.

Observers cautioned that the detailed cease-fire negotiations could still take considerably more time and must solve the difficult problem of where the opposing forces will be located in the country under a cease-fire.

After a final peace agreement here, the British would still face the task of actually obtaining the cease-fire in the field while setting up its transitionary government in the war-torn country and making certain that neither side tries to intimidate voters or seize power by force if it loses the election.

Although the new public positions announced today by the British and the Patriotic Front still left several differences between them, British sources said those gaps already had been narrowed in private negotiations. Front spokesmen also hinted at compromises.

The key remaining issues are:

The length of the transition period and election campaign. The guerrillas, who want time to get all their voters into the country, are now publicly seeking four months; the British and Muzorewa want two. Sources on both sides indicated that three months is a likely compromise.

The status of the Patriotic Front politicians. The guerrillas want to display to voters some trappings of power similar to those of Muzorewa and his Salisbury incumbents, who must give up power to the British governor but presumably will keep offices and cars. Patriotic Front spokesmen hinted that they expected something from the British on this.

The role and size of the Commonwealth force in monitoring the ceasefire. The British and the Front disagree over whether it should have the authority to intervene in armed disputes, but this and questions about the rival military forces can be left for the cease-fire phase of the conference.

Although the cease-fire negotiations involving the opposing military commanders are bound to be delicate, the momentum of the conference now makes a breakdown unlikely. All three sides have invested too much in the agreements reached so far to pull out now, according to diplomatic sources.

Carrington's method of inching up the curtain on Britain's plans for the cease-fire also has provided enough details of what comes next so that the guerrillas would be agreeing to the transtion plan knowing they can live with Britain's general approach to the cease-fire.

Carrington's approach has been first to gain concessions and agreement from Muzorewa and then come back to the Front, say there can be no further compromises and press for acceptance by the guerrillas. A series of deadlines and ultimatums last month finally resulted in guerrilla acceptance of an independence constitution, which removes major powers held by the 3 percent white minority in the population of 7 million, a major concession by Muzorewa and his white colleagues.

The foreign secretary used a similar approach to the transition. He first won Muzorewa's agreement to give up power during the transition to legal independence and then went to work on the Patriotic Front. This time he avoided specific ultimatums because he could not move into cease-fire negotiations without the Front.

Failure to agree on the transition plan would thus end the conference and force a British deal with Muzorewa, whose international acceptance would be in doubt. Britain would then have to assume temporary authority over a nation locked in a civil war that was bound to escalate.

This time, Carrington used Kaunda's visit to begin unveiling further British concessions to induce the guerrillas to accept the British plan, moves which Nkomo today called significant.

First, Carrington introduced the idea of a cease-fire monitoring force of about 1,000 troops from Britain and its former colonies in the Commonwealth. Later, he said the troops could stay inZimbabwe-Rhodesia after the election to insure stability. This was to reassure the Front that, if it won the election, it would not become the victim of a coup backed by the Salisbury forces.

Carrington next agreed to a suggestion by Kaunda that guerrillas who accept the cease-fire should be fed and housed by the interim British administration, giving the Front troops a stake in keeping the peace. Carrington also promised Kaunda that commanders of the two forces would have equal roles in a military commission supervising the truce.