The Rev. Bismarck Carballo, the Nicaraguan Roman Catholic Church spokesman who was barred by Sandinista authorities from returning home late last month, yesterday denounced the government in Managua and defended his own actions that led to his exile.

Carballo, speaking at his first press conference since he was prevented from boarding a plane to Nicaragua June 28, said the Nicaraguan government has persecuted the church, whose role, he said, is "over and above" politics but often is misconstrued as anti-Sandinista.

The ban on Carballo was part of a crackdown by the ruling Sandinistas following the June 25 vote by the U.S. House of Representatives to provide $100 million in military and humanitarian aid to antigovernment guerrillas, known as counterrevolutionaries or contras. On June 26, the government indefinitely closed La Prensa, the country's only opposition newspaper. On July 4, it expelled Bishop Pablo Antonio Vega, considered the most conservative and outspoken member of the country's hierarchy, accusing him and Carballo of sympathizing with the Reagan administration.

Speaking through an interpreter at a press conference here yesterday, Carballo said that the church supports neither side in the battle between the government and the rebels, and he called for a reconciliation among all parties in his strife-torn homeland.

In response to questions about the situation in Nicaragua, however, Carballo said the government had lost sight of the original tenets of the revolution that brought the Sandinistas to power in 1979 and which the church had supported. There was nearly univeral backing for the overthrow of the late Anastasio Somoza, for a revolution that would usher in freedom and democracy, he said. The government's new leaders, however, had "another project in mind."

Now, the populace largely supports the church in its struggle against the government, he said. "Ninety percent of Nicaraguans are Catholic. I am sure that this 90 percent is supporting its cardinal and its hierarchy."

Asked whether he favored U.S. aid to the contras and supported their efforts against the Sandinistas in Nicaragua, Carballo said that the church's goal is to disarm everyone and promote a dialogue of reconciliation, but that disarming only one side would not solve the country's problems.

He said that although he has been accused of "calumny against the revolution," he has spoken out only against the government's antagonism toward the church. "I don't consider that I am collaborating with any enemy," he said.

Carballo, 36, directed the Catholic Radio, which the government shut down Jan. 1, and has spoken for the generally conservative Roman Catholic bishops on many issues on which they are at odds with the Sandinistas.

A spokeswoman for the Nicaraguan Embassy here countered Carballo's assertions that the government has treated the church unfairly, accusing both Carballo and Vega of campaigning for the contras in the United States.

"The government of Nicaragua has not engaged in religious persecution," said Sarali Porta, the spokeswoman. "There is not a problem with religion. The problem is with the hierarchy of the church that have been advocating the contras."

At yesterday's press conference, held at the office of the U.S. Catholic Conference, Carballo said the government had acted against him and Vega "to take away the prestige of Cardinal Miguel Obando y Bravo ," Nicaragua's top Roman Catholic prelate.

Porta said in a telephone interview that "there is no campaign to discredit the cardinal," but added that Obando has "never, never" spoken out against the contra attacks in Nicaragua.

Carballo said he has used several diplomatic channels in seeking to return to Nicaragua, first by soliciting the advice of Obando, then by speaking with the National Conference of Catholic Bishops and the Vatican mission here. He said he hoped "publicity and world pressure" would cause the Nicaraguan government to readmit him.

In other criticism of the Sandinistas, a report released recently by the International League for Human Rights, a New York-based organization, charged the Nicaraguan government with systematic repression of human rights. The government frequently harasses, arrests and detains its opponents, dissident labor activists, religious leaders, independent journalists and human rights defenders, the study said.

Porta said the Nicaraguan Embassy has not yet received a copy of the report.