Chilean labor leaders went into hiding today to avoid arrest by government security forces and reiterated their intention to begin a general strike Thursday against the military government of President Augusto Pinochet.

Leaders of five major union confederations and Chile's transport unions, who pledged Monday to strike until the government "fundamentally changes its attitude" on a range of political issues, conceded this evening that government arrests of labor leaders, censorship of the news media and divisions in the opposition might substantially reduce support for the strike.

The labor militants said, however, that they hoped the work stoppage would gain momentum Thursday and the following day.

"The strike is on, there's no doubt of that," said Luis Sepulveda, the executive secretary of the Union of Democratic Workers, one of the confederations supporting the strike. "If the leaders are arrested there will be others waiting to step in."

Government officials, who arrested one strike leader and brought criminal charges Tuesday against five others now in hiding, had taken no further action by this evening to prevent the most serious opposition action yet attempted against military rule.

Political sources reported that Gen. Pinochet had been blocked in an attempt to initiate more severe action against the opposition, such as an imposition of martial law, by more moderate sectors in his government and by the Navy and Air Force.

Leaders of the strike command, who are expected to be summoned to appear before a judge Thursday, went into hiding to avoid arrest. Reliable sources reported, however, that they intended to meet tonight with U.S. Ambassador James Theberge to explain the strike and its objectives.

A series of jailings and strict censorship of the news media during the past several days appear to have sharply reduced the strike's chances for immediate success. Seven top leaders of the powerful Confederation of Copper Workers, which began strikes against the government last week, are under court-ordered detention and 11 other labor leaders, including six local copper union leaders, are being held by the government.

No reports on the proposed strike appeared today in Chilean media following a government crackdown described by opposition journalists as the most severe since the months after the military's coup against Marxist president Salvador Allende in 1973.

After one radio network, controlled by the opposition Christian Democratic Party, broadcast a strike call yesterday morning, its directors were summoned by officials and ordered to cease the reports. Chilean journalists said media directors have been threatened with arrest or the withdrawal of their publishing or broadcasting licenses for reporting the strike or other political news.

The strike movement followed massive demonstrations against the government in cities last week. It has also been weakened by lack of support from the political parties, which remain officially proscribed.

The Christian Democratic Party and other noncommunist groups are seeking to organize a broad coalition, including labor and professional groups, to continue the opposition's earlier and more moderate plans of calling a day of national protest each month.

"An indefinite strike has to be the final strike," one top party leader said in an interview, while asking that his name be withheld. "We are not in a position to bring down this government yet. It is a long process."

Labor leaders' strategy is to focus on shutting down travel and communications, thus paralyzing activity in this long, narrow country heavily dependent on road transport. A similar strategy a decade ago produced paralyzing work stoppages that helped bring down the Allende government.