The military government here has suspended publication of the country's leading opposition magazine, a signficant reversal of liberalization process that began early last year.

The decision to suspend publication of Hoy magazine for two months was announced Saturday by Interior Minister Sergio Fernandez with the approval of President Augusto Pinochet.

Fernandez cited interviews with two exiled Chilean politcians, both members of former president Salvador Allende's Socialist Party, as the direct cause of the suspension. Yet Fernandez also said that Hoy was being closed because it had consistently questioned the "authority of the government to define the framework" for Chile's return to civilian rule.

Hoy immediately asked the court to reverse the suspension. This sets up a test case that could either give legal sanction to censorship or greatly strengthen the press under the national security laws promulgated when the current authoritarian government seized power in 1973.

Regardless of the outcome of Hoy is likely to harm the government's efforts to improve its international image. Civilian Cabinet ministers, the country's ambassadors and pro-government groups in the United States have regularly cited Hoy as a prime example of press freedom here.

Hoy, which has the largest circulation of any magazine in Chile, provided an outlet for Christian Democratic and other opposition views. The magazine also printed numerous well researched and serious analyses of issues that embarassed the government, such as the secret police's involvement in the assassination of former foreign minister Orlando Letelier in Washington.

Its suspension comes at a time of increasing unrest in Chile's major universities, increasing activity among labor unions and a surge in terrorist activity directed at prominent government supporters and businessmen.

The closing of Hoy, which in Spanish means "Today," also comes at a time when Pinochet is about to announce his new constitution. It is to embody the military's ideas for a return to civilian rule under a system of "authoritarian democracy."

Many observers, including a member of Pinochet's Cabinet, said the decision to suspend Hoy reflected the president's growing irritation with its criticism. At the same time, Pinochet and other hard-line officials apparently want to demonstrate that the military government is still firmly in control.

The importance of the legal test growing out of Hoy's suspension has been recognized by the daily newspaper El Mercurio, generally a staunch supporter of the government. El Mercurio blasted the action, calling it "a grave error."

"Before public and international opinion, the suspension . . . will be wielded like a flag of war and will serve as antigovernment propaganda in circles far wider than the sphere which the suspended magazine could ever have influenced," it added.

El Mercurio said the military government's new constitution will never be viewed as legitimate if the military authorities do not at least allow minimum opposition criticism and some forum for debate.

Members of the opposition Christian Democratic Party, led by former president Eduardo Frei, have long argued that the military regime and its most respected supporters, the new economic elite led by Foreign Minister Hernan Cubillos, had wanted Hoy to publish both as an outlet for the opposition and to give the military regime a "benign face" to improve its international image.

El Mercurio and those around Cubillos had hoped to avoid a confrontation like the one that has occurred, believing that the opposition press would not get out of hand as long as the limits of press freedom were vague, according to several sources. At the same time, the government could have continued to point to Hoy as an example of the increased freedoms the military would tolerate.

In a rare public statement, Frei said this week that although the real season for Hoy's suspension "was to silence an organ of expression that was both independent and objective" at a time when the government is faced with several serious problems and is about to announce, besides the new constitution, other new policies that are likely to prove controversial.

Among the problems Frei cited was a court appeal by the United States on its request for the extradition of three former secret police officials allegedly implicated in the Letelier assassination.

Among the upcoming policy announcements Frei noted was a new labor code that might be unacceptable to unions in the United States and Europe and result in a boycott of Chilean exports. Frei said the government did not want an opposition magazine raising questions about these issues at a time when Chile's "international situation is so difficult."