The government of Gen. Augusto Pinochet, seeking to block opposition plans for a national protest next week, today authorized 88 political exiles to return to the country, including former leaders of the Christian Democratic and Communist parties.

In the second such action in less than three weeks, government officials said Renan Fuentealba, a former senator and party president of the centrist Christian Democrats, and Cesar Godoy Urrutia, a Communist former congressman, could enter the country. Last month the government authorized the return of six political leaders among 128 exiles.

The conciliatory measure was timed four days before a planned national antigovernment protest organized by the proscribed but still active political parties. The government's announcement was also accompanied by new measures of repression against internal opposition leaders. Last night, the offices of a prominent labor organization were searched and ransacked by security forces and at least five persons were arrested.

Pinochet and top military officials have insisted publicly that the protest, the third organized against the government in the last three months, will not be allowed to proceed. Last month's event led to massive demonstrations and violence in major cities and touched off strikes by labor unions that the government combated with arrests, media censorship and efforts at conciliation.

"The government has been tolerant in accepting the two protests that have occurred," Pinochet said last week. "But it's all over, gentlemen. In the future, all the legal remedies will be applied."

In recent days, government officials have acted aggressively to break up the protest organization and convince moderate and conservative sectors to ignore it. In addition to the search and arrests last night in the offices of the National Union Coordinate, police in riot gear quickly broke up a small demonstration by human rights activists, detaining at least 14 persons.

Earlier in the week, three persons, including two leaders of the youth organization of the Christian Democratic Party, were arrested and about 700,000 pamphlets announcing the protest were confiscated. Because of a recent government crackdown on the news media, newspapers and television stations have not mentioned the protest and only two radio stations have reported that it will take place.

Gabriel Valdes, president of the Christian Democratic Party, said this week that he had been threatened and that thousands of leaflets had been distributed describing him as a "traitor" manipulated by foreign interests.

Valdes charged the government with "the fomenting of an atmosphere of hatred and violence that naturally leads to the commission of crime."

[In Washington, State Department officials met with Chilean Pedro Felipe Ramirez, a member of a Christian leftist party and of the late president Salvador Allende's Cabinet. It was the first such meeting known to have taken place with a representative of a Chilean leftist party since the military coup of 1973.]