Three members of Nicaragua's revolutionary junta, representing forces that until recently were shunned by U.S. diplomats as pro-Marxist rebels, got a red-carpet tour of Washington yesterday that included meetings with President Carter and his potential rival for the presidency, Sen. Edward M. Kennedy (D-Mass.).

The reception accorded the trio underscored the all-out effort being made by the Carter administration to shift into a friendly relationship with the Sandinista-dominated guerrilla movement that in July wrested power from Nicaragua's longtime dictator, Anastasio Somoza.

In some quarters of the administration and Congress, there still are fears that the Sandinistas are an inherently Cuban-controlled force intent on turning Nicaragua into a base for communist penetration of Central America.

However, the dominant policy position within the administration has been to accept the junta's assurances that it has no hostile intentions against Nicaragua's neighbors and to try to move the country in moderate directions by offering U.S. friendship and financial help in rebuilding its civil-war-torn economy.

That was why the three junta members -- Daniel Ortega, Alfonso Robelo and Sergio Ramirez -- were accorded the unusual courtesy of a 30-minute White House meeting that included some of the administration's highest-ranking officials and that ended with handshakes and posing for pictures in the White House Rose Garden.

Joining Carter at the meeting were Vice President Mondale, National Security Affairs Adviser Zbigniew Brzezinski, Deputy Secretary of State Warren M. Christopher and other representatives of the State Department and White House staff.

Afterward, the junta members, who are en route to the United Nations General Assembly meeting in New York, went to Capitol Hill for a luncheon with the Senate Foreign Relations Committee and various other senators, including Kennedy, who dropped by to chat with the visitors.

Sources present at the various meetings said the exchanges were primarily of a get-acquainted nature, with the junto members seeking to reassure U.S. officials of their peaceful intentions and to discuss in general terms the kinds of reconstruction assistance they hope to win from the United States.

Nicaraguan sources said the White House meeting dealt almost exclusively with economic issues, including junta efforts to renegotiate nearly $600 million in foreign debt due primarily to U.S. commercial banks this year.

After the Nicaraguans had outlined their problems, the sources said, the White House arranged for them to hold an additional meeting at the State Department yesterday afternoon to talk about Nicaragua's financial problems.

The United States has provided nearly $8 million in emergency food and medical aid to Nicaragua, both during and after the civil war. Two weeks ago, the first direct economic assistance, nearly $9 million, was approved. Administration officials now are working on a long-range assistance package that would total approximately $100 million.

The administration also has offered to train some Sandinista troops at U.S. bases in Panama, but the junta, which originally had expressed interest in obtaining U.S. arms, since has indicated it has changed its mind and will not accept the military training offer.

Sources also said that at the White House meeting, Christopher, who supervises administration human-rights policy, praised the junta for adhereing to its promises to respect individual liberties within Nicaragua and to bar summary executions and other reprisals against Somoza's former supporters.

The reception given the junta members at the Senate luncheon was more mixed however. Sen. Edward Zorinsky (D-Neb.), chairman of the Latin America subcommittee and the luncheon host, told reporters afterward that the guests had been asked a number of blunt questions about their political views and their past activities.

The three, who share power with two other junta members, represent a cross-section of the different forces that came together to oppose Somoza. Ortega, the only one who actually is a Sandisista, represents a faction of the movement at odds with its more overtly pro-Cuban wing; Ramirez is a former academician identified with social democratic political ideas, and Robello is regarded as representative of the more progressive elements in the Nicaraguan business community.

In discussing the meeting, Zorinsky, who has been outspokenly friendly toward the new government, said: "There have been a lot of innuendoes and rumors. It's important that they be answered. But it's also important that we not prejudge a revolution by what has happened in other revolutions and judge it instead by the actions it actually takes."

A different view was offered, though, by Sen. Richard Stone (D-Fla.), who traditionally has taken a hard-line position against Cuban and other Marxist activities in Latin America.

Stone said he believed the new government should be given a chance to demonstrate its peaceful and democractic intentions. But he also said he was concerned about recurring rumors that Nicaragua plans to help guerrilla movements opposing the military-dominated regimes in neighboring El Salvador, Guatemala and Honduras.

Stone said that, in response to his questions, Ortega had denied that Nicaragua plans "to export revolution" to its neighbors and also had denied that he and his brother, Umberto, who was recently appointed head of the Nicaraguan armed forces, had received military training in Cuba.

These denials, Stone added, contradicted intelligence information he had received from El Salvadorean sources, and he added: "I'm afraid I still have my doubts, and I think we should check carefully on what happens down there before we commit outselves too heavily to assisting the Nicaraguan junta."

After repeated questioning by reporters, Ortega, who spent several months in Cuba after being imprisoned by Somoza for seven years, denied having received training in Cuba and characterized charges of potential Nicaraguan interference in other countries as "the type of provocation that reactionary forces would like us to become engaged in to provide a pretext for intervening in Nicaragua."