TEGUCIGALPA, HONDURAS, AUG. 18 -- Nicaraguan rebels, who initially voiced approval of a regional peace plan signed by five Central America presidents, are now concerned that their U.S. aid lifeline will be cut before democratic reforms called for in that plan are implemented by the government in Managua.

In the face of what they see as confusion in Washington over rival U.S. and Central American peace plans, the rebels, known as contras, are planning a round of contacts with regional presidents and with congressional and administration officials in Washington to discuss their reservations about the proposals and to try to resolve the aid questions, rebel leaders said.

They intend to propose to Washington that a new U.S. aid package be approved, but that disbursement be made conditional on the Sandinista government's compliance with an agreement to implement democratic reforms, the rebel officials said.

Both civilian leaders of the contras and fighters in the field are now expressing concern about the Central American plan signed this month in Guatemala, according to rebel sources here.

One factor in the confusion in Washington, as it is seen from Central America, appears to be a lingering Reagan administration commitment to its own plan for settling the five-year-old war between the contras and Nicaragua's Sandinista government.

This plan was issued on the eve of a Central American summit meeting in Guatemala City that resulted in the signing of a regional peace plan originally proposed by Costa Rican President Oscar Arias.

The Arias plan, which is aimed at ending conflicts in El Salvador and Guatemala as well as Nicaragua, has superseded Reagan's plan as far as Central America is concerned. Other Latin American countries have been rallying behind it, and appeals are being made to the European Community, Japan and other nations to support it.

"The Reagan plan was relevant in that it acted as a catalyst in binding together the five Central American presidents quite unexpectedly," said a western ambassador here. "But its usefulness from the Central American point of view is already past. The United States has to come to terms with the fact that a motley collection of Central American countries is finally coming of age."

According to directors of the Nicaraguan Resistance, the contras' political umbrella group, the specific steps envisaged in Reagan's plan are no longer valid in view of the signing of the Arias plan. But what is still important in the Reagan plan, they say, is the U.S. bipartisan consensus it represents and the prospect of continued military aid to the contras if the Sandinistas refuse to implement democratic reforms.

Meanwhile, contra leaders have been expressing concerns about the Arias plan, particularly its provision for an aid cutoff. As it applies to Nicaragua, the plan calls a cease-fire between the estimated 17,000 contra fighters and the 75,000-member Sandinista Army, a general amnesty, the cessation of foreign aid to the rebels, the elimination of contra bases in Honduras and internal "democratization" measures in Nicaragua including full press and political freedoms and internationally monitored elections. These provisions are to be implemented simultaneously 90 days from the Aug. 7 signing of the accord.

The major problem, said Alfredo Cesar, a member of the Nicaraguan Resistance directorate, is what happens between Sept. 30, when authorization for U.S. funding of the contras under a current $100 million aid package expires, and Nov. 5, when the Arias plan's 90-day deadline is reached.

"The key for us is how military pressure is going to go on while we pursue a diplomatic track," said Cesar, in Costa Rica, in a telephone interview. "The unilateral cessation of U.S. military aid is the major thing that bothers us."

He said he would shortly visit Washington to propose that the U.S. administration and Congress agree on new military aid for the contras, then figuratively "put it in a drawer with two keys" -- held by Reagan and House Speaker Jim Wright (D-Tex.). Aid for the contras would not continue if the Sandinistas made good their pledges to implement democratic reforms, Cesar said.

"This would show U.S. good will to advance the peace plan and comply with the cessation of military aid, while giving us time to negotiate and giving the Sandinistas a clear signal that a lack of good faith would unlock the drawer," he said. The contras are insisting on direct negotiations with the Sandinistas on a cease-fire, which they consider one of the most difficult provisions of the peace plan to achieve.

"We hope the United States approves the aid on the basis of proper compliance with the agreement," said Azucena Ferrey, another member of the Nicaraguan Resistance directorate.

She acknowledged that there are "divisions" in the directorate over the peace plan, but said this was "logical in a democratic group" and that "if we all thought the same way, we would be like the {Sandinista} Front."

The peace plan "has many holes," she said in an interview here. "And in the case of Nicaragua, it has not only holes, but craters."

Among the drawbacks, Ferrey said, was that the accord lacks a provision for a new Nicaraguan amnesty. Instead, it calls for application of an existing one, which she said was inadequate. Other contra leaders have complained of the lack of explicit sanctions for noncompliance and a failure to call specifically for cease-fire negotiations between the rebels and the Sandinistas.

"None of the Central American proposals for Nicaragua has ever taken into account the Nicaraguan people," Ferrey said. "The problems in Nicaragua are between Nicaraguans. It is a civil war."

According to contra sources, the peace plan has widened a fundamental difference in rebel ranks between those who believe in a political solution and those committed to a military overthrow of the Sandinistas. The former are represented essentially by Cesar and fellow Costa Rica-based directorate members Alfonso Robelo and Pedro Joaquin Chamorro, the sources say, while the latter are led by the more hard-line directorate members, Adolfo Calero and Aristides Sanchez.

A major reason for the Reagan administration's lukewarm response to the Arias peace plan is an unstated commitment to a contra military victory, Central American analysts say.

Contra sources say the commander of the largest rebel force, former Nicaraguan National Guard Col. Enrique Bermudez, believes that the contras can achieve a military victory in two years.