The Sandinistas and U.S.-supported rebels accused each other Friday of responsibility for the fourth breakdown in peace talks, and the rebels requested U.S. military aid in case the fighting starts again.

A banner headline in the Sandinista newspaper Barricada read: "Contras Are Sinking And Deny Peace."The rebel Radio Liberacion said: "The Sandinistas don't want agreements for peace and democracy."

At their last meeting Thursday, the two sides could not agree on how to implement their March 23 agreement on a permanent cease-fire and democratic reforms.

They did agree, however, to extend the truce in the 7-year-old war in effect since April 1 and not to engage in "offensive military operations."

A transcript of the Radio Liberacion broadcast quoted Contra leader Adolfo Calero as saying "the armed road is the only option left for democratization in Nicaragua."

It quoted U.S. congressional sources as saying a new aid package of up to $270 million would be presented to Congress soon.

At a news conference Friday in Washington, Calero said: "The only alternative we have in the face of those threats is to defend ourselves, and to defend ourselves we need military aid."

He suggested the United States provide about $105 million, the amount he said the Soviet Union has delivered to the Sandinistas this year.

Nicaragua's leftist government claimed Friday the rebels, known as Contras, wanted the three-day round of talks to fail so they could blame the Sandinistas and press the United States for more aid. The last U.S. military assistance to the Contras ran out Feb. 29.

According to the rebels, President Daniel Ortega's government wanted to rush the peace arrangements in hopes any aid requests would be voted down.

White House spokesman Marlin Fitzwater said Friday the Reagan administration was reviewing the possibility of aid but had "no decision or conclusion at this time." He blamed the Nicaraguan government for the breakdown in negotiations. "It is clear that the lack of progress is due to Sandinista intransigence over democratic reforms," he said.

The last Sandinista proposal Thursday clearly yielded to a Contra demand that democratic reforms come before the rebels lay down their arms, but the Contras said it did not go far enough.

It would have allowed eight Contras to participate with delegates from 14 political opposition groups in "internal talks" with the Sandinistas on such issues as freedom of expression, the right to strike and electoral reforms.

Those talks would be held before the rebels disarmed, but any agreements reached would be subject to approval by the Sandinista-controlled National Assembly.