A famous and popular leader of Nicaragua's Sandinista revolution surfaced here today after more than 10 months underground to denounce the direction of the government run by his former comrades in Managua and call for the ouster of unnamed Sandinista commanders he termed "traitors and assassins."

For more than two hours of impassioned rhetoric, Eden Pastora, the famous "Commander Zero," tore into what he described as the increasingly rigid and Marxist government he served until June 26 of last year as a high official and a vital symbol.

He spoke angrily of what he called the "humiliation" suffered by himself, the men who had fought at his side and "the Nicaraguan people" at the hands of the current Nicaraguan leaders.

Pastora, 45, condemned the "bourgeois" style of the nine powerful members of the ruling Sandinista Front's National Directorate, even though he was known for his own extravagant style in the first year after the revolution and today he wore a diamond ring and a gold watch.

"I will drag them with bullets from their mansions and Mercedes Benzes," Pastora vowed.

Pastora was intent on portraying himself today not as the ally of "counterrevolutionary" groups that include former members of the ousted Somoza dictatorship's hated National Guard, but as the authentic, if betrayed, voice of the Sandinista revolution itself.

He appealed to "the people in arms"--the Sandinistas' regular Army and the volunteer militias he once commanded--"to expel from power those whom the accusing and damning finger of national hero Augusto Cesar Sandino points out as traitors and assassins."

Both the U.S. government and domestic opponents of the current Sandinista leadership have been looking for a leader who could crystallize the discontent growing in Nicaragua as a result of economic hardships and often unpopular government policies. Someone was sought who had the necessary expertise and leadership, but was free of past association with the dictatorship of Anastasio Somoza.

Pastora would seem to fit the bill, since he became a symbol of the revolt against Somoza when he led a successful raid in August 1978 on the National Palace, becoming something of an international folk hero. The figure of the commander--gun raised triumphantly in the air--became the key image of the insurrection.

His resignation last year as vice minister of defense and virtual disappearance from the international scene raised questions about the unity of the revolutionary government and its immediate future that only began to be answered today.

The immediate impact of Pastora's remarks is unpredictable as he seems to be depending more on his reputation and his personal charisma than any immediately quantifiable amount of armed or disciplined support to back him.

He was accompanied, however, by several other disillusioned former comrades in arms, including Panamanian guerrilla-adventurer Hugo Spadafora, who could provide the nucleus for an armed push against the current Sandinista leadership.

Costa Rican reporters questioned Pastora nervously about whether he planned to use their country as a base for armed attacks on the Nicaraguan government as he did while fighting Somoza.

Pastora said he would wait for the reaction inside Nicaragua to today's press conference, adding: "Not yet."

Local newspapers said Pastora met with President Rodrigo Carazo and President-elect Luis Alberto Monge and has been granted permission to stay here.

Some of Pastora's supporters said privately today that they hope Pastora will be able to mobilize the same kind of broad popular support, politically and militarily, that characterized the 1979 insurrection against the dictatorship of Somoza that brought the Sandinistas to power.

There has been particular anger and fear in Nicaragua over the extent to which the country seems to have been dragged, by both its own leaders and the Reagan administration, into an East-West confrontation, and Pastora played on this concern today.

He criticized the fact that Nicaraguan pilots have been trained exclusively by the Soviet Bloc, that Soviet tanks for which a defensive army has virtually no use were acquired by the Sandinista leadership, and that Cuban uniforms are sometimes worn by senior Sandinista commanders.

In reference to an unspecified number of Cuban and other military advisers now in his country, Pastora said in his prepared statement that he is "calling on all Nicaraguans to put themselves on a war footing as long as there is a single foreign soldier on the fatherland's soil."

Clearly hoping to rally the Sandinista government's regular Army and the militias he once commanded to his banner of "true Sandinism," Pastora described those troops as "men and women of honor and love who constitute the only guarantee that the revolution is irreversible. Today I appeal to that honor and love."

Pastora also attacked "imperialism" of both East and West, citing as examples the cases of Vietnam, Afghanistan, El Salvador and Poland.

"Our Sandinism cannot allow us to be caught up in the East-West conflict, which is contrary to our national interests," he said.

Pastora went on to address all the points of Sandinista policy criticized by opponents of the government.

Echoing the desires of the nation's businessmen, Pastora called for "a political climate that stimulates production and investment."

He reiterated support for freedom of worship, which some Nicaraguans feel has been compromised, and freedom of the press, which has been the focus of intense domestic and international debate. The newspaper La Prensa repeatedly has been closed down and all local media have been censored since a "state of emergency" was declared a month ago.

"Commander Zero" blasted arbitrary seizures of land and property that have raised a furor among businessmen and landowners and denounced the jailing of Marxist revolutionaries who are "being punished for the grave crime of interpreting Marx with different criteria than their comrades in power."

The Miskito and other Indian groups of eastern Nicaragua have been "jailed and killed without there being a newspaper or radio that can denounce before the world this regime of terror that rules on the Atlantic Coast and in all Nicaragua through the feared State Security" police, Pastora said.

He publicly warned his former boss, Defense Minister Humberto Ortega, who once was viewed as a moderate and is now widely considered one of the most doctrinaire Marxists in the government.

"Either Humberto straightens things out or I will straighten them out," Pastora said in a booming voice.

Pastora did not say when he plans to return to Nicaragua.

He reportedly has taken up residence here with his family, which only succeeded in leaving Nicaragua in the last few weeks.

Some sources close to Pastora say that other Nicaraguan opposition leaders may also be gathering in Costa Rica and that former junta member Alfonso Robelo is here at least for the moment.