Conflicting reports emerged yesterday over whether Sovet leader Mikhail Gorbachev made a firm offer this week to President Reagan to suspend military aid to the Marxist Sandinista government of Nicaragua so long as the Central American peace process is going forward and the United States does not resume arms shipments to the contras.

According to several members of Congress who were briefed by Reagan yesterday at the White House on his talks with Gorbachev, the Soviet leader made the offer during an 11-minute walk on the south grounds of the White House Thursday.

Several Democratic and Republican members of the House and Senate leadership said Reagan discussed what sounded to them to be "a done deal" with Gorbachev on Nicaragua.

But there were differing accounts over what exactly had been said by the two leaders. For example, a senior White House official partly confirmed congressional accounts of Gorbachev's offer, but denied there was any "done deal," or that any U.S.-Soviet agreement had been reached.

"The president got some indications Gorbachev is willing to consider slowing up arms and money to the Sandinistas as long as both sides are willing to respect the Guatemala City agreement," the official said, referring to the plan by five Central American nations to end internal conflict.

But the official said Gorbachev "understood" how firm Reagan is in supporting the contras.

There were also conflicting reports as to precisely what Reagan had said about the Gorbachev offer and whether there was any real agreement. There was speculation that Gorbachev might have made the offer in hopes of eliciting a cutoff of U.S. military assistance to anticommunist rebels in Afghanistan.

Reagan and Gorbachev were discussing both Afghanistan and Nicaragua at the time, according to congressional and administration sources.

"It wasn't all that clear," said House Minority Leader Robert H. Michel (R-Ill.), who attended the briefing. "But the president did say they {the Soviets} would probably be limiting their support {to the Sandinistas} to small arms . . . no more planes or big artillery pieces."

But Michel added that "in no way" was Reagan backing off a policy of continued administration support for the contras.

House Speaker Jim Wright (D-Tex.) gave a slightly different version.

"President Reagan seemed to believe that the Soviet Union is willing, in the context of the peace initiative, to withdraw Soviet personnel and weapons and not to send any more. This is the impression that the president got. Also, this is the impression I have gained after talking to Sandinista officials," he said.

According to another congressional account, Reagan said Gorbachev offered to end shipments of heavy weapons and withdraw Soviet advisers if the peace process continues, and asked Reagan to end U.S. aid to the contras on the same condition.

Another account said there was no mention of a withdrawal of Soviet advisers, only of heavy Soviet weapons.

But two of those present agreed that Reagan said he told Gorbachev that the administration has no intention of supplying the contras with anything other than humanitarian assistance and transportation items so long as the peace process continues -- reflecting what Congress is likely to support in any case.

House Democrats have made it clear they will oppose additional military aid to the contras if there is any chance for the peace process to succeed. Senate Republicans are advocating $22.8 million in nonlethal aid for the contras until February, while Senate Democrats are proposing only $5 million.

Another administration official said Gorbachev first brought up the subject of Nicaragua at a lunch Wednesday with Reagan when he made "a rather cryptic statement," or "casual comment," about the possibility of the Soviets cutting off arms supplies to Nicaragua in the context of U.S.-Soviet cooperation in implementing the Arias peace plan, named after the Costa Rica President Oscar Arias.

The Arias plan formed the basis for the later Guatemala City pact, which calls for a ceasefire, amnesty, political dialogue and nonintervention by outsiders in all five Central American countries.

This official said Gorbachev did not pursue the idea then and the U.S. side had taken it as a serious offer.

The two leaders discussed regional conflicts Wednesday morning and again at their lunch Thursday, and also set up a working group of experts who met for six hours Tuesday and Wednesday. However, U.S. officials indicated Afghanistan and the Iran-Iraq war were the main subjects and have hardly mentioned Nicaragua in their briefings.

Reagan and Gorbachev went out of their way in their joint summit statement to stress the persistence of "serious differences" in their talks on regional matters. Reagan said they had discussed those differences "bluntly" and Gorbachev complained at his news conference, "I can't say that we have made much headway."

The U.S. side had been hoping Gorbachev would announce a "date certain" for a Soviet withdrawal from Afghanistan and also respond to American entreaties for a joint U.S.-Soviet effort at the United Nations to impose an arms embargo on Iran to force an end to the Iran-Iraq war.

Instead, Gorbachev at his news conference went no further than to reaffirm what Afghan President Najibullah said before the summit -- that Soviet troops could be withdrawn in 12 months or less. The Soviet leader also bluntly rebuffed a U.N. arms embargo of Iran.

Even so, diplomatic activity on both fronts is expected to pick up with U.N. Afghan peace negotiator Diego Cordovez traveling to Moscow Monday for talks on a possible formula for an interim government in Afghanistan involving the Soviet-backed Kabul government, the U.S.-backed anticommunist resistance and independent leaders.

Cordovez met here yesterday with Undersecretary of State Michael H. Armacost to receive a summit briefing.

Staff writers David Hoffman and Don Oberdorder contributed to this report.