The Chilean government has closed down a radio station critical of its policies, basing its action on the station's ownership by the opposition Christian Democratic Party.

The silencing last week of Radio Presidente Balmaceda was the second major blow in two weeks to the rapidly diminishing group of independent radio stations and magazines that are the vestiges of Chile's once free-wheeling press.

The weekly newsmagazine Ercilla, the last mass-circulation publication not controlled by partisans of the military government sphere in mid-January with the departure of its managing editor, Emilio Filippi, a Christian Democrat.

Ercilla and Balmaceda commanded enermous audiences for their coverage, which contained analysis and criticism of events in Chile that the newspapers, all of which are controlled by supporters of the military government, would not print.

The 3 1/2-year process of bringing the once ideologically varied Chilean media into step with the country's military rulers has included censorship, closure and confiscation of newspapers and radio stations, suspensions, arrests and expulsion of dissenting editors.In the case of Ercilla, it was simply a case making publisher a generous offer.

Radio Balmaceda had been the object of intermittent censorship in the past, but the latest measures closes it for the duration of Chile's state of emergency, which has been in effect since September 1973.

The radio went off the air after about 30 policemen were deployed at its Santiago studios, according to radio personnel. Radio workers were blocked from entering.

The closure order was from the office of Brig. Gen. Julio Canesa, who is in charge of enforcing the state of emergency in Santiago.

Canesa's decree said the Junta's 1973 decrees imposing a "political recess" on the Christian Democrats "expressly forbid them from . . . antipatriotic works, and any form of interference in civic and civic activities."

It was common knowledge that Radio Balmaceda is owned by the Christian Democratic Party, but the ownership had not been found objectionable in the past, even during degrees temporarily suspending its broad casts in 1975 and 1976.

Besides the four previous closures, the radio had submitted to prior censorship for brief periods in 1975, and last year the station's manager was arrested and banished for three months to a town of 600 inhabitants in the Andes mountains near the Bolivian border.

Ercilla and Radio Balmaceda are part of a dwindling group of news media that carried coverage of human rights and economic issues that did not agree with the official government position.

The group includes three other radios - two privately owned and one owned by the Catholic Church - and the Jesuit monthly magazine Mensaje. All the rest of the Chilen press, radio and television is either government-owned or controlled by strong political and financial supporter of the government.

Censorship was officially discontinued a year after the overthrow of Salvador Allende, but has occasionally been invoked since then. Self-censorship media supervision carried out by the government are sufficient, editors say, to keep news content and discussion of government policy within strict confines.

Partially to compensate for the control of information and lack of political forums, a growing network of informal publications has been set up by Chilean dissident groups.

A free-swinging, extremely partisan press was for decades a major ingredient in the political ferment that swept Chile from rightist to centrist to leftist governments and back again.

Ercilla changed hands in September when a group of pro-junta financiers bought out owner-publisher Sergio Mujica. According to sources at the magazine, Ercilla had been subjected to mounting pressures by the government, including substatial losses incurred when the government forbade the circulation of an issue that had already been printed. The purchase price reportedly was $850,000.

Fillipi, after an effort to work with the new owners, walked out last month with most of the editorial staff, protesting "incompatibility."

Ercilla's success began in 1968 during the government of Christian Democratic President Eduardo Frei. Fillipi turned the staid, rightist-tinged newsweekly into a progressive, readable guide to Chile's increasingly complicated political an social processes - and into a whopping financial success as it grew into the largest circulation weekly in Chile.

It was in outright opposition to leftist President Allende during the political upheavals from 1970 to 1973 that led to a military coup.

Chile's press freedom was branded "licentiousness" by the new military rulers and their, and the press was one of the first targets of the purges. Four left-leaning newspapers and a newsweekly that had supported the Allende government were immediately closed and confiscated.

A Cristian Democratic intellectual journal, Politica y Espiritu, was closed by the government in late 1975 after it repeatedly touched taboo topics, such as the secret police, and published a detailed proposal for an alternative economic policy to the rigid free market being implemented by the junta economic team.

In developments this week, a Santiago appeals court for the first time granted a habeas corpus writ for release of a Chilean who was listed as missing but actually was in the hands of the secret police.

In addition, the Supreme Cpourt ordered a special investigation of the whereabouts of 13 other missing persons whose families contend that they were arrested by the secret police in December.

The decisions represent a major advance in the legal battle by the Catholic Church and families to clear up the fate of hundreds of persons who have disappeared since 1973.

The habeas corpus writ freeing Carlos H. Contreras Maluje also ordered that criminal charges of illegal arrest be brought against agents who detained him in November.