The government of Gen. Augusto Pinochet, reacting to a call by labor leaders for a general strike, pressed criminal charges against six opposition leaders today while announcing it would permit the return of several well-known political exiles.

In a significant concession to opponents, government officials announced that they would permit the return beginning Wednesday of 128 exiles, including centrist Christian Democratic Party leader Andres Zaldivar and five other former political leaders. It was the first time the Pinochet government has permitted the return of prominent opposition political leaders, including associates of the late president Salvador Allende, from exile.

Also included on the list distributed by the Interior Ministry was Isabel Letelier, the widow of Orlando Letelier, the former diplomat and minister killed in a 1976 car bombing in Washington allegedly by operatives of Chilean secret police. Isabel Letelier now works at the Institute for Policy Studies, where her husband was employed. She was permitted a visit to Chile in 1978.

Hours after announcing the conciliatory measure, the government arrested the head of the key truckers' union and filed charges against four other labor leaders who called a strike for Thursday to protest military rule. Also charged was Jorge Lavandero, a former Christian Democratic senator, who leads a coalition of opposition politicians.

The twin measures on exiles and protest leaders appeared to increase the difficulty of Chile's opposition in organizing the first general strike ever attempted against the Pinochet government. The move also continued a government strategy of attempting to isolate leaders of a week of unprecedented antigovernment protests while offering concessions to rank-and-file workers and moderate-to-conservative political sectors.

While human rights groups and Christian Democratic leaders welcomed the impending return of the exiles, they described the measure today as arbitrary in its selection of leaders and inadequate to address the issue of Chilean political exiles. The government has said there are 10,000 forced exiles while human rights groups' estimates run to 35,000.

The government's initiative also seemed to have little effect on the determination of the officially proscribed parties and the labor unions to continue organizing the national strike.

Even as the Interior Ministry announced lifting of the sanction against Zaldivar, who has been prohibited from entering the country since October 1980, his brother Adolfo was releasing a statement by 54 political party activists calling for Pinochet's resignation and scheduling of elections for a national assembly in six months.

The Christian Democratic Party and other political leaders have supported Monday night's strike call by six labor organizations representing at least 200,000 workers. The groups said they were protesting government repression and the lack of essential freedom and would continue the strike until the government "fundamentally changes its attitude."

By tonight, however, it was unclear to what degree the opposition would be able to carry out the planned shutdown. Police today arrested Rudolfo Quinteros, the president of the truck drivers' union, and officials sought court-ordered detention of four others leading the strike organization. The labor leaders along with Lavandero remained free tonight pending court hearings expected Wednesday.

Seven national leaders of the Confederation of Copper Workers were already in detention on charges of calling strikes in mining centers last week. At least six other local union leaders were reported by the copper union to be under arrest today, and two of the four state-owned mines, El Salvador and Chuquicamata, remained under military authority.

Labor union officials also said that four other labor leaders in the opposition had been arrested and were being held incommunicado. The copper confederation charged that three of the leaders were being held by the National Center of Information, Chile's secret police. Diplomats said all four were believed to have links with the Chilean Communist Party.

In addition, censorship rules issued to Chilean media by government authority appeared to have severely limited public support of the strike plan. While four Chilean radio stations broadcast news of the labor announcement last night and early this morning, the reports ceased later today and the strike was not mentioned by newspapers or television.

Political leaders and diplomatic analysts said the strike may now draw only modest support from Chilean workers, but added that it appeared to have forced the Pinochet government toward measures of political liberalization it has staunchly resisted in recent years.

Responding to repeated appeals from human rights groups and conservative government supporters, Pinochet created a commission last year to study the return of exiles.

In the last six months 561 persons had been permitted to return. In the past, however, authorities have not granted entrance permission to opposition political figures. Pinochet rejected recommendations by the exile commission that many leaders be allowed to return, human rights groups and diplomats said.

Today's list of eligible returnees included three former activists in the governing coalition of Socialist president Allende, who was overthrown by the military in 1973. They were former senators Rafael Tarud and Rafael Gumucio and former interior minister Carlos Briones.

Also named was Claudio Huepe, Christian Democratic ex-congressman, and Eugenio Velasco, a member of the Radical Party who served as a lawyer for opposition politicians before expulsion in 1976.

[Velasco, who from exile in Washington had made repeated pleas to return to Chile "before my children forget their native land," said he now hopes "to make my presence felt in Santiago" on a visit. But he said his exile left him with no job or house there.]

[After a lengthy search, he recently found employment at the Inter-American Development Bank to support him, his wife and two younger children in Washington. After so long a wait, he concluded, "I cannot afford to return" permanently.]

Mrs. Letelier said, "I am very glad to be able to go visit my country and very grateful for the courage of the working class of Chile . . . but I can't be happy until all exiles can return."

Sergio Bitar, a fellow at the Wilson Center and an ex-minister in Allende's Cabinet, was not on the list. He described the announcement as "a small triumph, won thanks to the determination of Chile's workers." He said he and others in Washington would visit the Chilean Embassy Thursday to ask that they, too, be allowed to return.