The month-old settlement talks on Zimbabwe-Rhodesia hung in the balance today after the Patriotic Front guerrillas refused to give their unqualified approval of a country.

British Foreign Secretary Lord Carington adjourned today's 90-minute meeting and for the first time did not set a time to reconvene the talks involving Britain the colonial power, the warring black nationalist front and the Zimbabwe-Rhodesian government.

Despite the crisis atmosphere, many observers said they felt that a diplomatic solution to the problem would be found, allowing efforts to solve the 14-year-old Rhodesian independence question to continue.

It was the third confrontation this week between Britain and the Patriotic Front, but the continuing brinksmanship has succeeded in significantly narrowing the differences over the issue.

In a sense, the immediate problem is a procedural one.

Britain demands full agreement on the constitution before going on to the second-and more difficult-part of the conference: the transition to legal independence, including disposition of the rival military units and a cease-fire leading to an election. The Front wants to reserve its position on several issues in the constitution, pending the outcome of the entire conference.

The Front fears that a separate agreement could lead Britain to go ahead and implement the constitution just with Zimbabwe-Rhodesian Prime Minister Abel Muzorewa should the conference fail to agree on transition arrangements.

Muzorewa already has accepted the constitution.

All sides in the test of wills are subject to international pressures not to allow the breakdown of the conference, often regarded as the last chance for a negotiated settlement. the alternative is escalation of the seven-year-old war, which has already killed more than 20,000 people, and the risk of East-West involvement in the struggle for black majority government.

Joshua Nkomo and Robert Mugabe, leaders of the Front, issued a statement at today's meeting, outlining the remaining major constitutional differences. They involve entrenched protection of land and pension rights for the white minority and the amount of white representation on key governmental commissions.

"We are now satisfied that the conference has reached a sufficiently wide measure of agreement on the independence constitution to enable it to proceed to the next item on the agenda," they said.

"If we are satisfied beyond doubt as to the vital issues relating to transitional arrangements, there may not be need to revert to discussion on the issues we have raised under the constitution."

The key word was "may." Carrington asked the Front leaders several times whether that word, in effect, could be changed to "will," but they would not go beyond their statement.

At one point, according to British spokesman Nicholas Fenn, Nkomo said the statement was "clear and straightforward." Carrington replied, "I wish I found it so."

Finally, after a 35-minute private meeting among Carrington, Nkomo and Mugabe, the foreign secretary said he could not accept the Front's reservations and added that major matters were still outstanding.

Therefore, he said, "I have no alternative but to adjourn. When we resume, which will be in the near future, this must be to discuss the arrangements for implementing the constitution. Before that I shall need to know without ambiguity whether the Patriotic Front accepts that constitution. k

"I hope i will get a satisfactory response and that Mr. Nkomo and Mr. Mugabe will consider carefully what I have said."

Carrington, who first called for definite acceptance of the constitution by both sides eight years ago, said he was giving the front "a little further time."

A Front spokesman said, however, "Are we prepared to recondsider? No, there's nothing to reconsider here."

Spokesmen for both the Muzorewa government and the Front said they expected the talks to continue and that their leaders would remain in London for the negotiations.

British sources said they did not expect the adjournment to be a long one, and added that the Foreign Office may attempt to draft new language to get around the procedural problem.

In a move that could lead to a further narrowing of differences, Britain made a gesture today that could satisfy some of the Front's complaints over land ownership, the key remaining issue.

The guerrillas oppose a provision prohibiting seizure of land without compensation for 10 years. The Front maintains the war is being fought over land, that white settlers originally took it from blacks and the new government would not have sufficient funds to pay compensation. Some 6,000 whites in the 7 million population own 86 percent of the arable land.

In a carefully phrased statement, Carrington made a tentative offer of financial assistance.

Britian, he said, "will be prepared, within the limits imposed by our financial assistance.

Britian, he said, "will be prepared, within the limits imposed by our financial resources, to help." He cited the possibility of assistance for settlement schemes and agricultural development projects but would give no specific amount.

In a speech two days ago, Mugabe made it clear that such aid would be welcome under certain conditions. If such aid is made avalable, he joked, "We will fight to the death for the white farmers to receive copnesasatoin."

In another narrowing of differences, it was noted that in its list of remaining problems the Front left out any reference to the citizenship issue. The guerrillas have contended that persons who became Rhodesian citizens since the illegal declaration of independence by the white government in 1965 should not automatically retain citizenship.

Richard Moose Jr., U.S. assistant secretary of state for African affairs, discussed the negotiations here yesterday during a stop en route to East Africa. Moose reiterated the United States' support of Britain's conduct of the conference, the U.S. Embassy reported.