Bayardo Arce of the ruling Sandinista Front today described as "absolutely irreversible" the Nicaraguan government's decision to hold elections Nov. 4, despite a major opposition group's refusal to participate unless the vote was postponed.

Arce made his comments in a news conference after a breakdown in talks with opposition presidential candidate Arturo Cruz aimed at delaying the polls.

"I am sorry to say that there will be no participation by the Democratic Coordinator because the second registration period closed yesterday without their registering," said Arce, the political coordinator of the front.

Arce and Cruz are here ostensibly for a meeting of the Socialist International, two of whose leaders, ex-chancellor Willy Brandt of West Germany and ex-president Carlos Andres Perez of Venezuela, expended major efforts to bring the two Nicaraguan sides together.

Brandt and Perez stressed that the International's efforts would continue, suggesting that today's statement by Arce may not be the last word on the elections issue.

Arce said that in this third round of talks the opposition Democratic Coordinator alliance injected "a series of demands that had nothing to do with the electoral process."

At a press conference after the conclusion of the Socialist International meeting, Arce said the demands included "the release of all prisoners of war and mercenaries captured in hostilities" and a condemnation by Managua of the Soviet Union and Cuba. Arce said this would violate the Sandinista foreign policy, which he described as nonaligned.

Cruz rejected Arce's account of the breakdown in talks and denied that any such issues had been discussed.

Conference delegates said the initiative to break off had come from Arce, and that he had probably overreached his authority in attempting to negotiate a delay in elections while Nicaraguan head of state Daniel Ortega was firmly opposing such a move. In an interview yesterday in New York, Ortega had said no delay would occur.

The talks here followed two earlier sessions in which basic agreement had been reached on a series of issues for the election, such as location of ballot boxes and free TV time during the campaign, according to Perez of Venezuela, and these agreements had been ratified by top Sandinista leaders.

Arce justified the suspension of talks by saying that Nicaragua was threatened by the Reagan administration and that a new offensive, designed to sabotage the electoral process, was planned against three cities.

Arce also said would-be candidate Cruz had declared publicly he would seek a commitment from the rebel forces to lay down their arms in exchange for acceptance of his terms for participation in the vote.

Adolfo Calero, leader of the Nicaraguan Democratic Force, a rebel group fighting the Sandinistas, said in a telephone interview from Costa Rica that his group supported the Democratic Coordinator's position on elections and was willing to enter into a cease-fire if the Coordinator's conditions were met. If an agreement was not reached, he said, the rebel group would continue to fight to overthrow the Sandinistas.

In an interview before Arce's news conference, Cruz said that agreement had been reached on all major issues such as press censorship, and the only remaining stumbling block was the opposition's request that the deadline for registering candidates be extended "three or four more days."

"We have reached agreement on all parts of the plan of Colombian President Belisario Betancur except for how the postponement of the elections will take place," Cruz said. "We have agreed on the basic rules for free elections -- freedom of movement, freedom for the press, international observers and access to information during the election process. Ballot boxes will be placed where citizens can vote without fear: away from the eyes and ears of the political commissars and not in the barracks.

"However, there are some conditions attached to postponement of the elections. The directors of our alliance decided we are in no position to meet a midnight, Oct. 1 deadline, and have submitted a letter to the Supreme Electoral Council asking for a few days' postponement. The request for a few days' postponement is to give time for the mission to return from Rio to Managua. It remains to be seen if the Sandinistas will agree to grant such an extension."

One American delegate said the breakdown appeared to be a result of bluff from the Sandinistas, who after granting concessions had banked on Cruz backing away from final agreement.

Closing the Socialist International, Brandt said he had formulated an urgent appeal to Ortega and to Cruz asking both to look into the "large areas of agreement reached in Rio" and to follow up what had been discussed.

Perez read into the meeting's record the draft agreement said to have been accepted by both parties. He said the Sandinista front had given all the guarantees requested by the opposition alliance but that the Democratic Coordinator in Managua had requested a delay to allow Cruz to return with the document, and this had not been accepted.

Perez said the Socialist International had not renounced its efforts. "We believe this is a tremendous effort" which would later allow elections to take place," he said.