Using captured Palestine Liberation Organization rifles supplied by "a contact" in Europe, freshly financed by mysterious friends in Mexico, Venezuela and Panama, and with increasingly open help from members of the Costa Rican police forces, the troops of Nicaraguan rebel leader Eden Pastora are once again in action against the Sandinistas.

Only 10 days ago Pastora, known as Commander Zero, called a "unilateral cease-fire" to "reevaluate our resources" after Washington appeared to ignore his group's open appeal for funding. His people talked about their desperate lack of food, clothing and guns. The move was widely viewed as the beginning of the end of the fight for him and the Democratic Revolutionary Alliance, the organization whose troops he leads.

Now Pastora is mounting his most ambitious offensive operations since openly taking up arms a little more than two months ago against his former comrades in the Sandinista National Liberation Front that rules Nicaragua. His forces say they have encircled the town of San Juan del Norte in the southeastern corner of Nicaragua's Atlantic coast. If it falls, they would be the first anti-Sandinista force to take a municipality.

Alfonso Robelo, political director of the Democratic Revolutionary Alliance--known as ARDE--said at the group's office here that he did not know and did not want to know what lay behind the maze of clandestine connections, black-market arms deals and mysterious benefactors that had "given us enough oxygen to breathe again."

They "could well be" fronts for covert funding from the U.S. Central Intelligence Agency, Robelo said. "I wouldn't ask. Who cares?"

Neither would Robelo say how much the new funding amounts to, but he estimated that ARDE requires $200,000 to $300,000 a month at the very least to keep its forces in operation.

But despite the obvious optimism around the ARDE office here, these on-again, off-again actions illustrate one of the group's greatest weaknesses, even in the eyes of other Nicaraguan exiles sympathetic to its objective of ending what it calls the Sandinistas' communist rule while preserving "the Nicaraguan revolution."

"They improvise everything," said one of Pastora's frustrated friends. "It's an adventure, not a project. They don't have any strategic plan."

These critics suggest that while impetuosity and machismo are certainly part of Pastora's charisma and made him a national hero when he was fighting with the Sandinistas against the dictatorship of Anastasio Somoza, they will not serve him effectively against the more sophisticated Soviet- and Cuban-trained forces he may now confront.

Sandinista leaders in Managua, who affect disdain for the man they call "the traitor Pastora," say they believe he expected them to make the same mistake Somoza did of tying up their best troops against him in the quagmires of southern Nicaragua. To avoid falling into that trap, they said, they have sent very few troops into the remote jungle regions near the Costa Rican border where Pastora currently claims control of about 65 miles along the San Juan River that forms the border with Costa Rica and anywhere from 30 to 80 miles into the interior.

The current offensive against San Juan del Norte and its garrison of from 75 to 100 Sandinista troops could force a larger commitment from Managua.

But Pastora's people clearly view the fall of San Juan del Norte, if it happens, as more than just a victory over the Sandinistas. It would mark a psychological and political triumph over other anti-Sandinista rebels in the north, the Nicaraguan Democratic Force.

Until now, most or all of Washington's extensive backing for the fight against the Sandinistas has gone to this group, whose military leadership is made up of members of the Somoza dictatorship's defeated National Guard.

Robelo said one of the reasons he was given in Washington for the lack of U.S. aid to ARDE was that the entire budget for such things until the end of the fiscal year on Sept. 30 is devoted to backing the anti-Sandinista troops in the north.

Pastora has refused to form any alliance with these former enemies working out of Honduras despite reports of considerable pressure from Washington to do so. But there was also a long-term interest, stated privately by Washington officials, in keeping Pastora "clean" of the U.S. taint. In the competitive world of the counterrevolution some Democratic Force leaders were concerned only a few months ago that they would do most of the fighting only so that Pastora could step in and take advantage of it.

San Juan del Norte, isolated and small though it may be, would be the first municipality to fall to any anti-Sandinista force. The Democratic Force's efforts to take Jalapa in northern Nueva Segovia province or other similar objectives have been unsuccessful so far, although they have taken and held for several days a hamlet called Porvenir.

Pastora's people say that by taking San Juan del Norte they would also be in undisputed control of several miles of coastline as well as the San Juan River, thus enabling them to bring in more supplies with greater ease.

Robelo said yesterday at an interview in the ARDE office here that when Pastora officially began military activities against the Sandinistas on May 1 he had only 380 men with him, carefully infiltrated over a long period of time. Now, Robelo said, as many as 2,000 may have joined up and Pastora's inability to supply the new recruits led to the pleas for help and the cease-fire ploy last month.

In the course of June, however, more than 1,000 rifles and other arms were received in various shipments, according to Robelo.

These included "several hundred" Soviet-design AK47 rifles captured from the PLO by the Israelis and then funneled into clandestine arms supply networks, Robelo said. The specific deal was cut, Robelo said, through a contact in Europe on the condition that no inquiries be made about their original source. "But that's not unusual," Robelo added.

Other weapons, including M79 grenade launchers and M60 machine guns, are American-made but not directly supplied by the United States, Robelo said.

"If somebody comes to us in Munich and asks us if we want a shipment of arms," Robelo said, "we say yes. We don't ask a lot of questions."

Recently, he added, money has been even more desperately needed than guns. The cease-fire was called on June 22, Robelo said in a second interview today, because "we were totally broke." The necessary cash finally came through from some of the same contacts in Venezuela, Mexico and Panama who have helped with the acquisition of arms, he said.

Speaking of possible forces behind these sources, Robelo said, "If it is Argentina, if it is the Israelis, if it is the South Africans, who knows and who cares? What we ask for is help." But he said all such aid must be unconditional.

None of the support that ARDE has received comes directly from any government, Robelo said. Speaking of Venezuela and Mexico, however, he added, "It could be from politicians in a government, yes. Governments do not act openly."

Similar clandestine arrangements appear to be at work here in Costa Rica. Only a few weeks ago Costa Rican officials reportedly confiscated ARDE's only helicopter and revoked Pastora's visa. But in the Colorado area near the mouth of the San Juan River, tourists and reporters have seen men identified as Pastora's troops given open cooperation by members of the Costa Rican Rural Guard. Officers in ARDE have been known to fly to the mouth of the river from San Jose and then travel by boat to meetings with Pastora in a matter of hours.

While the administration of Costa Rican President Luis Alberto Monge remains carefully neutral, Robelo said, "We do receive collaboration from the Costa Rican people and that would include people who have positions in the government.

"They have come to realize that we are fighting a war in Nicaragua so that there will be no war in Costa Rica," Robelo concluded.