PANAMA CITY, JUNE 12 -- The military-dominated government of Panama enforced a broad blackout on independent news media today, the second day of a general strike called to oppose the rule of Gen. Manuel Antonio Noriega.

The indefinite press clampdown, part of a state of emergency that began yesterday, was one of several measures to end four days of protests and street fighting in Panama, a key military, banking and commerce center for the United States.

The blackout took effect only hours after the U.S. Embassy had released its second statement in four days stressing that "freedom of expression is key" to Panamanian democracy.

The main opposition daily, La Prensa, remained closed after halting its presses late yesterday in response to a government censorship order, editor Winston Robles said.

The government, controlled by top military commander Noriega, decided yesterday afternoon to appoint censors to review at least four publications before they were printed, Robles said. The move apparently was to thwart news of continuing rioting in some working-class communities despite the presence of hundreds of rifle-armed soldiers in the streets.

The tabloid Extra, which is affiliated with La Prensa, and a weekly, Quiubo, also stopped publishing rather than submit to censorship.

Another independent paper, El Siglo, decided after receiving the gag order to print a final edition with a headline saying, "See You Later!" But, according to editor Jaime Padilla, soldiers arrived to force him to stop the presses and removed page dummies to the Interior Ministry. The censor probihited the publication of the farewell headline, so the paper did not go to press.

Two independent radio stations, Continente and Mundial, were shut down. The remaining stations were broadcasting only news prepared by the state-controlled radio and progovernment editorials. Managers of all the television stations canceled their news programs yesterday and today after the government told them not to run stories about the protests.

Under Noriega's guidance, the government has gained control of dozens of radios and at least four Panama City dailies. This morning those papers carried banner headlines proclaiming, "Total Calm Returned to the Capital" and page after page of pictures of Panamanians going about their business as if nothing had happened.

La Prensa editor Robles said the paper's circulation doubled overnight after Sunday, when it began to publish interviews with Noriega's former deputy, Col. Roberto Diaz Herrera, who accused Noriega of being involved in assassinations and electoral fraud. In an interview at noon yesterday, Noriega denied the government would seek to censor the papers or that it had closed down any radio stations.

Radio Continente went off the air Tuesday when electricity to its transmitter was cut off. Since then, Panama Defense Forces troops have broken into and ransacked its administrative offices, according to Noris Correa, sister of its owner.

Noriega said the station had gone off the air because "of thick tear gas and the crowds running around near its offices." Radio Continente commentator and legislator Mayin Correa took refuge at midday yesterday in the Argentine Embassy here, her sister, Noris, said. A job training school belonging to Mayin Correa, a vociferous government critic, burned down Wednesday.

A spokesman for the Chamber of Commerce, Alfredo Castillero, said the general strike, called by the opposition coalition Nationalist Civic Crusade, was 65 percent effective in Panama City today. Almost all banks and most retail stores remained closed.

At a mass this morning attended by many opposition politicians, a Roman Catholic vicar, the Rev. Fernando Guardia, announced that the church has adopted an activist role in the current conflict. The church has joined the Nationalist Civic Crusade in what it calls an advisory role.