In gestures apparently designed to put international pressure on Nicaragua's Sandinista government and to broaden support for the troubled "counterrevolution," two major exile factions have called on the "Contadora" group of Latin American countries to help negotiate sweeping changes in Nicaragua's "Marxist-Leninist" government.

At a press conference here today, three exiled former leaders of that government called on the more radical Sandinistas governing in Managua and the U.S.-backed rebels fighting them to end their war and "rescue the revolution." They demanded an end to the "Sovietization" of the country and also asked for the restoration of the principles of pluralist democracy and a mixed economy for which they said the 1979 insurrection was fought.

Meanwhile, the Nicarguan Democratic Force, the most powerful of the armed groups fighting against the Sandinistas, released a letter to the foreign ministers of Mexico, Panama, Venezuela and Colombia. These countries, known collectively by the name of the Panamanian island, Contadora, where the ministers first met to discuss the problem, are seeking to end the region's widening violence through negotiations.

The Democratic Force asked the foreign ministers to sponsor a "dialogue" in Caracas on "the terms to end the civil war and establish the peaceful coexistence of all Nicaraguans in a free democracy."

But while the stated objectives of both the Democratic Force and the former Nicaraguan government leaders who spoke here today are similar, their political connections and approaches are radically different. Two of the three men here, former junta member and ex-ambassador to Washington Arturo Cruz and former customs chief and deputy commerce minister Leonel Poveda, have been closely tied to the apparently faltering movement of the Sandinista hero-turned-rebel, Eden Pastora. Until recently, when its representatives made open and apparently unsuccessful appeals for unconditional U.S. backing, Pastora's force had hoped to find the resources it needed among sympathetic liberal governments in Latin America or the members of the Socialist International.

The third man at the conference, Alfredo Cesar, avoided public connections with any group after leaving his post as the Sandinista head of the central bank to go into exile a year ago. Angel Navarro, another signatory of today's statement, did not attend the conference.

The three men insisted there was no intention of providing a pretext for escalating the U.S.-backed fighting if Managua rejects their initiative. Instead, one of them explained after the conference, it is intended to take advantage of some small indications of Sandinista flexibility.

At times there was an almost self-consciously Quixotic aspect to the whole affair at the Torremolinos Hotel. The response to the initiative may be "more bang-bang in the vacuum or a little echo," Cruz said afterward. "We had to try."

The Democratic Force, on the other hand, is financed by Washington and initially was trained by U.S. and Argentine advisers. It is led militarily by ex-members of the ousted Somoza dictatorship's National Guard.

The most intransigent of the groups fighting the Sandinistas, it has also been the most isolated internationally. Despite the support of Washington and the Honduran government, or perhaps because of it, the Democratic Force has suffered from an image of an artificially created movement.

Its support from Washington, moreover, is assured only through September. Its leaders originally expected to be well on their way toward victory by then. But they have found themselves increasingly limited, since early June, to operations around Nueva Segovia Province in the north.