The powerful Confederation of Copper Workers called a strike for Friday following the arrest this morning of the leader of nationwide antigovernment demonstrations.

Gen. Augusto Pinochet's confrontation with a labor-based opposition movement escalated with the strike announcement tonight by the 23,000-member copper union. Chile's largest and most politically important labor union also said it would consider continuing the strike Monday. One copper mining center voted to begin its strike Thursday.

The call for what would be Chile's first illegal national strike in a decade of military rule came following the government's arrest of Rodolfo Seguel, the 29-year-old leader of the copper workers and the coalition of labor organizations that called yesterday's national day of protest against Pinochet's rule.

The arrest came only hours after the end of demonstrations by tens of thousands of persons who barricaded streets, stoned police, destroyed property and banged pots and pans in cities across Chile.

At least two deaths and 13 wounded from gunshots were reported today by protest organizers, police and Chilean news organizations from the demonstration, the largest and most violent since the military took power in September 1973. Bombs and fires reportedly damaged several government buildings as well as shops, homes and dozens of bus stops, buses and cars. More than 1,000 persons were reported arrested across the country.

Government authorities, who called the protest a failure and part of an international conspiracy against the military government, prompted the sharpening of the political struggle today by expanding an already pending court case against Seguel.

This afternoon, 15 hours after police detectives broke down the door of the house where Seguel was staying, a judge ordered his pretrial detention on charges he incited actions that threaten national security.

In response, the copper workers' union kept a public vow to strike if any of its leaders were jailed. Union leaders also demanded the release of three other miners arrested yesterday and the rehiring of 23 workers dismissed at the mining center of Salvador, 700 miles north of Santiago, for actions linked to the protest.

Union leaders and political analysts said the proposed strike would lead to a major test of strength between opposition unions and the Pinochet government, which has been buffeted by economic crisis and declining political support for more than a year.

Four labor confederations linked with the copper workers in the National Command of Workers for the Protest were scheduled to decide Thursday whether to join the strike, which could bring the action up to 200,000 workers from every sector of the Chilean economy.

One of the confederations indicated tonight that it would join the protest. But labor officials and analysts said that it was not clear that all of the unions would support an illegal strike or that workers would stay home in large numbers.

"This is very difficult. In all of these areas there is unemployment and there could be unions that don't respect the strike," said Hugo Estivales, the acting head of the copper workers and the national command. He later added, "If the workers don't defend their leader, it will be the end of the labor movement in Chile."

There was no immediate official response from the government to the strike call, but some labor leaders said they believe Pinochet expected an unsuccessful strike would break the momentum of the growing protest movement led by the unions, which have organized two national days of protest in the past two months.

Although organized by the labor movement, the two protests have been joined by political parties, professional organizations, human rights groups and thousands of Chileans from all classes.

While deploring the widespread outbreak of violence, protest organizers and other opposition leaders today appeared jubilant over what they said was a clear signal of the government's deteriorating political position.

"The magnitude of the social protest is showing the consensus of rejection by the people for the political, economic, social and cultural situation that we are in," said a statement of the protest command.

"There has been a qualitative change in the participation of the masses--a radical change," said a leader of the outlawed Chilean Communist Party, which is blamed by the government for manipulating the protest movement. "This has put an end to all the old arguments over whether it is possible to have an open social protest against this government."

Despite the quick growth of the open protest movement, however, opposition leaders warned today that they did not expect Pinochet to be forced from power in the near future and said they doubted that the 67-year-old leader would even move to accept any of their other demands, which include economic reforms, changes in labor laws and an easing of restrictions on dissent.

"We have been asking for dialogue to the point of exhaustion, but the dialogue has not arrived and the government has taken us to the situation we are in now," said Estivales.

"The government does not have any alternative but to respond with force, with increased repression." he added.

Pinochet and other government officials called the demonstrations a failure but warned of a strong government response.

"If it is necessary I will toughen the government," the president said yesterday evening in Copiapo, a small town 480 miles north of Santiago where he had traveled shortly before the demonstrations began. Pinochet later added that "as a peaceful protest, the day was a failure because it ended in acts of vandalism and violence."

Despite such official statements and the arrest of Seguel, the extent of the government's action remained unclear late today. No exceptional security measures were announced, and despite expectations by labor leaders that Seguel would be expelled from the country immediately, the government appeared to be limiting its action to expanding the pending charge against the leader in civil court.

Conservative Chilean leaders, who have recently shown increasing dissatisfaction with Pinochet but generally opposed yesterday's protest, are urging the government to seek conciliation with its opponents rather than increasing repression.

"What is needed is an agreement between the armed forces and the civilian sector to resolve these issues," said Luis Valentin Ferrada, a leader of a right-wing movement that believes Pinochet should remain as president. Ferrada added, however, that the government had shown "no sign" of seeking to conciliate with critics on either the left or the right.