The warring parties in Zimbabwe-Rhodesia agreed today on an agenda for the British-sponsored settlement conference and did so in a way that provided hope for progress in solving the 14-year-old issue.

Both the Zimbabwe-Rhodesia government and the Patriotic Front guerrillas, locked in bitter warfare 5,000 miles from the ornate Victorian mansion where their leaders are meeting here, gave some ground. The agenda provides for discussion on both a new constitution and transitional arrangement leading to independence and makes agreement on one dependent on the other.

Although so far this first accomplishment in the three-day-old conference is simply one of semantics, it could have a significant effect on the outcome of the conference.

Britian, still technically the legal ruling power in the breakaway colony, called the conference to agree on a new constitution. The Patriotic front, however, insists on an overall peace conference. It says changing the constitution, which allows significant white control, is only one element in ending the escalating war that has killed more than 20,000 people since 1972.

On the surface at least, the Front, led by Joshua Nkomo and Robert Mugabe, came out ahead by gaining agreement that the issues are linked and that there can be no agreement until all the issues are resolved.

The Zimbabwe-Rhodesian government of Prime Minister Abel Muzorewa has regarded the conference as one to deal solely with the constitutional issue, hoping that agreement on the constitution would provide the government with long-sought international recognition and lifting of economic sanctions.

The Salisbury government won the point that the constitution should be discussed first. The Patriotic Front won the formal acceptance of the other issues and the linkage.

The fact that both sides gave ground and did not engage in their usual hostile remarks about each other in press statements on this issue gave support to the British hope that they have come to the conference to negotiate constructively. The conference is the ninth major attempt to solve the problem of Rhodesia and past efforts often have failed over similar seemingly small matters of semantics.

In addition, there was evidence of a thaw in the frostiness of the first two days when the talks lasted only 100 minutes.

British spokesmen said there were "moments of lightness" as the delegates mixed and shook hands during a one-hour coffee break that led to the compromise on the agenda. They termed the atmosphere of the session "reasonably accommodating," after characterizing the first two days as "businesslike."

Reporters were even treated to the irony of Patriotic Front spokesman Edison Zvobgo saying that Ian Smith, the white former prime minister and archenemy of the guerrillas, "helpfully supported" the Front's position on the agenda.

It was clear, however, that agreement on the agenda was only a very small first step and that there are many formidable hurdles before the problem can be resolved.

Some indication of that came tonight when the Muzorewa delegation sought a one-day postponement of the conference to consider detailed constitutional proposals submitted to both sides by British Foreign Secretary Lord Carrington.

Late tonight there was still no word on whether Carrington would grant the request but it was thought likely since the Patriotic Front had received a half-day postponement yesterday.

Zimbabwe-Rhodesian officials said they needed more time to examine the 15-page proposal that Carrington submitted to provide a basis to begin the constitutional discussion.

Details of the proposals were not released but they are bound to involve removing blocking power in Parliament exercised by the 230,000 white minority and curbing of white control of key government commissions. The issue is of major significance to the white-supported government, since whites form the backbone of the military and the economy.

The constitution is not as big an issue for the Front. It is assumed that Britain will press for the curbing of white control, since Prime Minister Margaret Thatcher already has criticized the current constitution worked out by Smith and Muzorewa as "defective."

For the Front, the key issues are how the country is administered during a transitional period leading to independence and particularly who controls the Army and police. One of the major reasons it refused to participate in the controversial April elections that put Muzorewa in power was that the poll was carried out under the protection of the Rhodesian military.

Carrington provided the key link between the two issues when he told the conference: "The British government understands and accepts for both sides that agreement on the constitution must be dependent also on agreement on arrangements for implementing it, in other words on pre-independence arrangements."

Spokesman Zvogbo said the Front felt "uneasy" without an agreed agenda that would show "the ground that has been covered and the distance to go" so the conference could not be adjourned by one delegation after agreement was reached only on the constitution.

His fellow spokesman, Willie Musarurwa, explained the Patriotic Front's concern. "What would happen if agreement is reached on a constitution but not on transitional arrangement? Wouldn't the British be tempted to implement the constitution (with the Muzorewa government)? Where would we be? Everybody would say we were asses for refusing to go along with what we accepted."