A conservative opposition member of Nicaragua's legislature has sought asylum in the Venezuelan Embassy here, Venezuelan diplomats said.

Felix Pedro Espinosa, a deputy from the Non-Official Conservative Democratic Party, scaled the embassy's chain-link fence at dawn Tuesday and was taken inside later by staffers, a Venezuelan official said yesterday in a telephone interview.

Espinosa, whose party holds five assembly seats, was the first opposition deputy to seek foreign asylum since the legislature began work in January 1985. The legislature, which is dominated by the ruling leftist Sandinista party, voted Tuesday to strip him of his legislative immunity, accusing him of ordering the burning of his own ranch house in an effort to embarrass the government. He has denied the charge.

Since the U.S. House of Representatives voted June 25 to approve $100 million military and nonlethal aid for the rebels, known here as counterrevolutionaries or contras, the Nicaraguan government has clamped down sharply on its public opposition at home.

Yet western diplomats here said the Nicaraguan government is losing support among European and Latin American nations by venting its anger on a civilian opposition that, like Espinosa, is increasingly powerless and isolated from the majority of Nicaraguans.

A range of opposition leaders here said in interviews this week and last that, with the increased U.S. backing for the antigovernment guerrillas, they see prospects for peace, and for their form of peaceful dissent, dwindling.

They said the main strength of their position now is simply to remain in Nicaragua, and even that is becoming difficult.

Espinosa sought asylum just hours before a justice commission of the 96-seat assembly issued its findings in a case in which Espinosa is accused of ordering the burning May 10 of his ranch house in northern Esteli province.

After a four-hour debate Tuesday afternoon based on the findings, which were unfavorable to Espinosa, the 61-member Sandinista delegation voted to strip him of his legislative immunity from prosecution and order him to stand trial for arson.

In an interview last week, a gaunt and worried Espinosa described the charges as "a complete absurdity." The cattle rancher charged that Sandinista security police had obtained false, coerced statements implicating him from two of his employes after holding them incommunicado for two weeks.

The lifelong Conservative Party activist said he suffered losses worth hundreds of thousands of dollars on a farm that was not insured. Sandinista leaders said Espinosa had the farm torched to blame the government and embarrass it.

Espinosa said he believed the Sandinistas were seeking to drive him out of his home province to block him from expanding his party's activities in a region troubled by attacks by the contras.

Rocked by the vote for contra aid, which is expected to pass the Senate soon, Sandinista leaders have gone on a full-scale war footing, calling this "the time of definition." They insist that Nicaraguan organizations must close ranks around their revolutionary program, warning that organizations that do not will be regarded with suspicion of being in league with the contras.

Opposition leaders here said the U.S. Congress gave the Sandinistas an excuse to limit the opposition's room to maneuver even more than they had before.

"We are in a spiral of polarization, and the U.S. aid tends to encourage further restrictions on our political space," said Erick Ramirez, head of the Social Christian Party, the largest opposition party.

"Ronald Reagan is the Sandinistas' worst enemy and their best friend," said Mauricio Diaz, head of the small Popular Social Christian Party, which sometimes sides with the Sandinista National Liberation Front, the ruling party, and sometimes goes against it.

"Each opposition party stands alone like a little feudal castle," added Diaz, whose party split from Ramirez's group in the mid-1970s.

A western diplomat described Nicaragua's opposition parties as "a shattered group of disputatious political midgets."

Last week, six opposition parties held a press conference to say the contra aid would "presage more violence and suffering for Nicaraguan people." They called on the government to form a peace commission to negotiate a cease-fire between Sandinista forces and the contras.

Asked by a reporter what chance the party leaders saw that the government would heed their proposal, Mario Rappaccioli, head of one Conservative Party faction, responded, "It would be a miracle."

"We are always the spectators and victims in the confrontation between two larger powers," said Luis Rivas Leiva of the Social Democratic Party. He was referring to the United States and the Soviet Union, which recently delivered at least 10 new Mi17 military transport helicopters to the Sandinista Army.

Of 13 parties in Nicaragua, six oppose the leftist government from more conservative viewpoints. Four of them are allied with labor and business groups in the Nicaraguan Democratic Coordinating Group, which does not participate in the Sandinista government or assembly. Four Marxist-inspired parties criticize the government from the left.

Many parties now in the opposition were crippled politically in 1979 when they were outstripped by the Sandinista Front in competition for leadership of the revolution against Anastasio Somoza.

The Sandinista Front confirmed its dominance as a majority party in November 1984 national elections which, though intensely controversial, were described as clean by most observers.

Espinosa is one of five deputies from his branch of the Conservative Party, now split into four factions. His was one of about 20 opposition votes in the assembly. Espinosa has presented three motions in 18 months. All were "crushed," he said.

"We thought at least we could use the assembly as a platform of protest," said Espinosa, camped out at a friend's law offices in Managua before seeking asylum at the embassy. "But we have been reduced to practically nothing."

His party joined the assembly's work on a new constitution for Nicaragua, but now has pulled out, along with another opposition party.

Opposition leaders noted that the frequent friction in rural villages between their supporters and Sandinista sympathizers has grown more dangerous since late last year. Four Social Christian Party members have died since November, the party alleged, as a result of beatings or mistreatment they received from Sandinista authorities. Twenty-three members were said to be in jail.