As President Reagan and Democratic opponents fight for the swing votes that will decide whether Congress continues aid to the Nicaraguan rebels, both sides are expected to make differing claims about whether Central America's democratic leaders regard the contras as a help or hindrance to regional peace.

Nicaraguan President Daniel Ortega, meeting the presidents of Costa Rica, El Salvador, Honduras and Guatemala last weekend, promised immediate steps to bring his Sandinista government into greater compliance with the five-nation peace agreement signed Aug. 7.

Administration officials and congressional leaders have said the outcome of votes on contra aid Feb. 3-4 will be determined largely by perceptions in Congress of Ortega's sincerity about implementing his promises.

They also agree that a significant factor in shaping these perceptions will be the other four leaders' signals about whether continued contra aid will move the Sandinistas toward greater compliance or cause them to scuttle the accord.

Congressional Democrats, convinced that the latter is the case, said they plan to contend that a vote for more contra aid is a vote to halt the peace process. At a meeting with reporters Monday, House Majority Whip Tony Coelho (D-Calif.) said of this strategy:

"This is not Ronald Reagan against Daniel Ortega. Ortega's agreement is with his four colleagues, and they'll determine if he is living up to it. For us, the question is whether we'll respect the integrity and wishes of the other four presidents, who are our democratically elected allies, and stop treating them like banana republics."

At the meeting, Rep. Lee H. Hamilton (Ind.), one of five Democrats who were observers at the five-nation summit in Costa Rica, said it is likely that, if Congress approves more contra aid, the Sandinistas will desert the peace process.

While the other four leaders do not think as one, Hamilton said, he believes that none is willing to abandon hope that the accord can bring stability to the troubled region.

These include, he said, El Salvador's Jose Napoleon Duarte and Honduras' Jose Azcona, who are hostile to Nicaragua.

In short, Democrats contend, while some Central American leaders might prefer maintaining the contras as a viable insurgent movement or a bargaining chip to end Nicaraguan interference in their affairs, they realize that they cannot have it both ways.

Other than Costa Rican President Oscar Arias, principal author of the peace plan and an outspoken opponent of contra aid, all of the Central Americans have tried to say as little as possible about the forthcoming congressional votes.

The Democrats contend that, if the leaders were forced to choose, they would favor halting contra aid at least until Ortega's compliance with his latest promises has been tested.

If so, that runs counter to Reagan's almost daily barrage of speeches and statements calling contra aid an "insurance policy" necessary to keep pressure on the Sandinistas to move toward democracy and away from regional subversion.

In hopes of making their argument more acceptable to skeptical members of Congress, the president and senior administration officials have said they will seek a relatively modest amount of aid, primarily nonlethal, to keep the movement viable while the world waits to see if Ortega acts in good faith.

They have sought to create the impression that this view is supported at least tacitly by Nicaragua's neighbors. As a statement issued in Reagan's name said Tuesday:

"At the Costa Rica summit, there was a clear consensus among the four Central American democratic presidents that the Sandinistas had not complied with the peace accord. By making his last-minute promises, President Ortega implicitly acknowledged the accuracy of that judgment."

In addition, while the statement implied that the other presidents agree with Reagan on continuing contra aid, none has said so publicly despite a plea by Lt. Gen. Colin L. Powell, the president's national security adviser, two weeks ago.

In fact, the Powell mission backfired because, despite strong administration denials, it enabled Coelho and other Democratic opponents to question whether the White House was attempting to bully the Central Americans.

Administration officials have since offered alternating arguments: Central Americans' views are not important on an issue that should be decided by how it affects U.S. interests, or most of the regional leaders support the contras but cannot say so because of domestic political considerations.

The latter is partly correct, particularly in Honduras and El Salvador, but neither country's leaders seem ready to risk admitting that.

This adds to the administration's difficulty in countering Hamilton's contention that Central America does not view further contra aid as ensuring peace but as something whose "effect would be a continuation . . . and an escalation of the war with results we could neither predict nor control. It also would mean that the Arias peace process would come to a halt."