Hundreds of Salvadoran military policemen and National Guardsmen carrying automatic weapons burst into five hospitals and 20 clinics of the state-run health system around the country before dawn today to end four-week-old takeovers by striking health workers.

The armed forces reported that four police "observers" -- unarmed and not in uniform -- were shot and killed in the action at San Salvador's General Hospital under uncertain circumstances. But neither the military nor the strikers reported that any civilians were killed or wounded there, and fragmentary reports from outside the capital listed no casualties.

The police actions appeared designed to crack down on what President Jose Napoleon Duarte charges is "subversive" use of the union movement by El Salvador's left-wing guerrillas to destabilize his government.

The state health workers' strike technically was illegal, but government officials acknowledged that such stoppages have been tolerated since 1979 without use of force. Duarte lashed out at unions in his state-of-the-nation address yesterday in a wide-ranging criticism of the Salvadoran left.

Leftist rebels condemned the government raid over their clandestine Radio Venceremos, pledging to respond by launching "a new transportation blockade within the next few hours and increasing economic sabotage attacks on electric power lines," United Press International reported. Little later high-power electricity cables in western Sonsonate province were dynamited, resulting in a blackout in much of the country, the Energy Company said.

The government also sought to show that it could use muscle without resorting to the brutality of which the three military security forces have been accused in the past.

"We've tried to do everything with the professionalism that the armed forces now have achieved," said Lt. Col. Enzo Rubio, who commanded the units that entered General Hospital.

Neither Rubio nor witnesses provided a clear account of how the "observers" were killed, although strikers suggested that they somehow had been shot by other police.

The government said that patients who had left the hospital during the union takeover had reported that the strikers had pistols and possibly a machine gun, but the strikers denied it. Rubio said "four or five weapons" were found, but he did not put them on display.

At General Hospital -- where the government called a group of mostly U.S. correspondents to be present during what was termed a "dislodgment" -- a special team and more than 100 military security agents bound the hands of several hundred hospital workers with twine and forced them to lie on the floor. The workers, including doctors and some nurses, were released after their identification documents were checked. The union's secretary general and another leader were arrested.

Workers, other employes and patients said they heard firing from the direction of the General Hospital emergency room for about 20 minutes after the police assault began nationwide at 3 a.m., and three large pools of blood were found at the room's entrance. But Rubio said he did not have full information about the shootings yet, and others interviewed seemed to be deliberately vague in a tense situation. The colonel, a National Police commander, said he acted after receiving a judicial order.

The strikers maintained emergency services and some normal medical operations during their takeover, which backed demands for a $75 monthly wage hike for all workers. The current minimum monthly wage is roughly $125. Strikers, whose union belongs to a left-leaning federation, also called for lifting of the state of siege and resumption of government peace talks with Marxist-led guerrillas and exiled leftist politicians.

Detained workers, and some other employes and patients, protested that the military had used excessive force. "How can someone enter a hospital like this? What about human rights?" one nurse said.

Strikers nonetheless cheered Rubio at the auditorium meeting, where he told them that his agents had received specific instructions to avoid force. "I don't know if anybody was beaten," Rubio said quizzically, and shouts came back, "No," "No, nobody." But moments later, strikers were shouting, "Torture," and raising their hands to show where they had been bound.