Senate leaders broke off talks yesterday on a bipartisan compromise to aid the rebels fighting the government of Nicaragua, with Democrats saying the White House "torpedoed" a possible agreement and Republicans accusing the Democrats of being inflexible.

With Republicans still claiming enough votes to gain approval of $100 million in aid for the Nicaraguan rebels, also known as counterrevolutionaries or contras, today's debate and vote on the key foreign policy issue of the election-year session begins with two major differences between the parties.

The White House and GOP leaders continue to oppose a requirement for mandatory bilateral talks between the United States and the leftist Sandinista government, and they object to a requirement that Congress vote again to approve the spending of most of the funds after diplomacy is given another chance.

After compromise talks broke down after three hours, Republican leaders predicted a much closer vote today. "I think it's possible to pass it," said Sen. Richard G. Lugar (R-Ind.), adding that the GOP had the 51 votes needed for passage. "It's going to be close," he said.

Sen. Jim Sasser (D-Tenn.) blamed the breakdown on John M. Poindexter, a Navy vice admiral and President Reagan's national security affairs adviser. Poindexter arrived late at a morning congressional negotiating session and stated the administration's position on the two issues in what Democrats said were unswerving terms.

"The admiral, he steamed in there at flank speed and just simply said we're not going to have any negotiations with no preconditions and that's it," Sasser said. "Before he got there, we felt like there was some give-or-take on it," he added.

Sasser accused the administration of "shopping for additional votes" instead of seeking a real compromise, and said he sensed "a hardening of the attitude emanating from the White House" after reports of a Sandinista troop incursion into neighboring Honduras.

Dennis Thomas, a top Reagan aide, accused the Democrats of headline-grabbing. "I wish there was as much effort to seek a good middle-ground as there is to get the evening headlines," Thomas said.

Lugar, chairman of the Foreign Relations Committee, said the talks broke off after Democrats indicated that they were unwilling to bend on the two contested points.

Majority Leader Robert J. Dole (R-Kan.), who also said the GOP had enough votes to prevail, held out hope that last-minute modifications could bring in some swing votes.

He was wary, however, that some changes to win moderates might lose votes among conservatives. "We could have some people going in the front door," Dole said, "and others going out the back door."

The breakdown in discussions appeared, however, to jeopardize Republicans' hopes to garner as many as 70 or 80 votes to claim a strong bipartisan mandate and strengthen their hand with the House, which rejected an initial contra aid request by a margin of 12 votes last week.

Senate debate began with some of the same no-compromise arguments that had marked consideration of the measure in the House last week. But much of the animosity caused by the administration's anticommunist rhetoric and predictions of another Vietnam was missing.

"I don't think we have to choose between being called patriots or being labeled appeasers," said Sen. Lloyd Bentsen (D-Tex.) as he announced his support for contra aid.

Sen. Edward M. Kennedy (D-Mass.) called for a cutoff in any assistance to the rebels. To approve more funds, he said, would be "plunging ahead down the path of more war and more bloodshed."

Sen. Patrick J. Leahy (D-Vt.) warned against being "swept away by war fever" that might accompany reports of the Nicaraguan incursion into Honduras.

He said a compromise might include "soothing words," but would not explain why America "is getting deeper and deeper into a squalid insurgency against an impoverished country of less than 3 million people, mostly illiterate peasants who don't have the remotest idea of what communism is, and who have never had a chance at real democracy."

Bentsen, however, termed the Sandinistas "well-armed Soviet clients" and said "it's not the United States that refuses to give peace a chance."

"Either we are in favor of helping the Nicaraguans throw off communist oppression or we are not," Sen. Jesse Helms (R-N.C.) said.

Helms said any compromise that ties release of most of the funds to the report of an observers' commission and "empty rhetoric about 'negotiations' " would primarily benefit "the other side, the Marxist side."

Senate leaders had hoped to wrap up most of the floor debate by early evening and vote late last night. But the Senate, after the breakdown in negotiations, put off the debate and vote until today. The Senate is scheduled to leave tomorrow on a 10-day Easter recess.

The two sticking points -- mandatory bilateral negotiations and an affirmative second vote -- have been points of contention throughout the discussions.

Dole said early in the day that negotiators would try to "finesse" some language on the bilateral talks.

Sasser and others argued that the United States must talk directly to the Sandinistas because these are the two "major belligerents" in the conflict.

The administration has argued, however, that such talks would strip from the contras any legitimacy they have, and contended instead that the Sandinistas must talk with the contras. The Sandinistas have said they will never do that.

The White House proposal would allow expenditure of $25 million immediately and the remainder of the funds 90 days later if the president determined that certain conditions were met.

Congress could avert final expenditure if it voted disapproval, but the White House could veto that resolution of disapproval.