Each week, the editors of the news magazine Hoy gather in one of the cluttered rooms of their aging, converted house here to read a letter from a man who has become their most influential critic.

Hoy is a magazine sympathetic to Chile's democratic opposition, and its most important reader is the military government's director of communications, Jose Miguel Amendariz. Each week, a curt missive from Amendariz -- accompanied by marked-up copies of the magazine's page proofs -- spells out which of Hoy's articles, headlines and pictures have been summarily censored under the state of siege.

The resulting file of correspondence is a remarkable record of how military authorities have used their six-month-old crackdown, nominally imposed to combat terrorism, to shut down Chile's once-thriving independent press. While banning six other opposition magazines from appearing at all, authorities have prohibited Hoy from publishing more than 50 articles and scratched quotations from public figures including U.S. Secretary of State George P. Shultz, members of the military's own junta and Chile's 19th century independence hero, Bernardo O'Higgins.

Hoy's editors say there is one particular word that has almost invariably drawn a strike from their censor's yellow felt-tipped pen: transicion. In Chile's political context, the term usually refers to the gradual move promised by the government of Gen. Augusto Pinochet toward a limited democracy.

Now, however, "transition" appears to be no longer tolerated in any context. Thus, a headline in Hoy referring to the Soviet Union's "transition" during the illness of former leader Konstantin Chernenko was clipped. So was a report on a kindergarten program to help young children judge television advertising. In the latter case, it turned out, the writer unwittingly had referred to kindergarten students as "children in a stage of transition."

"The idea of the authorities seems to be to show that they have absolute control over the media and that we have no chance to work independently," said Emilio Filippi, Hoy's managing director. "So they not only censor us, but they do it in an entirely arbitrary way."

Amendariz, who did not respond to several interview requests, recently told the Chilean magazine Cosas that the censorship was necessary "to put an end to what could well be called 'verbal terrorism.' "

"Liberty of expression," he added, "is a superior value that the government is the first to respect."

Increasingly, however, Chilean journalists and politicians argue that the curtailment of free speech has emerged as the most important aspect of Pinochet's hard-line campaign -- and the primary motive for the government's move this month to extend the state of siege for another three months.

"Censorship is practically the only motive for the state of siege," said Filippi. "As it turned out, that has been the most effective measure for demobilizing the democratic opposition."

While government repression against political opponents has appeared to be carefully limited in recent months, the crackdown on the press has been the most extensive since the months after the 1973 military coup. In addition to closing the six opposition magazines and censoring Hoy, authorities warned all other media not to report any news on politics and other subjects that might cause "public alarm."

To enforce the new guidelines, ranking government officials have telephoned Chilean newspapers and radio and television stations, often on a daily basis, to dictate how news should be covered. News organizations that dispute the orders have been threatened with shutdowns, according to several local editors.

The result has been a nearly complete blackout of all information about the opposition, human rights, some social initiatives by the Catholic Church and critical analysis of the deteriorating economy. Newspapers and magazines still publishing have suffered a precipitous drop in readership, and rumor-passing has become a major activity in the capital.

Journalists of the banned magazines defiantly have started four clandestine news bulletins, including two mimeographed dailies. Their combined circulation, however, is believed to be no more than 2,000 copies, in contrast to the more than 50,000 copies sold by each of several magazines last year.

"Before, there was a kind of political dialogue between government and opposition sectors through the press," said Marcelo Contreras, the director of the banned magazine APSI. "Without us, there has been no dialogue or national debate."

Even more importantly, moderate opposition parties have found that their ability to communicate with most of their followers -- and with each other -- largely has been destroyed.

"Restrictions on the press in this country simply mean the end of the opposition," said Ricardo Lagos, a top leader of the Socialist Party and centrist Democratic Alliance.

Many journalists and political leaders here now believe Pinochet's government will seek to maintain the media restrictions indefinitely. Facing strong pressure from foreign governments and internal allies to lift the state of siege, government officials are believed to be planning new decrees that will allow them to continue banning and censoring media while formally satisfying the demand for liberalization.

As one alternative, government lawyers have prepared legislation that would allow authorities to ban publications under a legal "state of emergency," the lesser condition in force in Chile for years before the state of siege was declared, according to sources close to the government. Currently, the state of emergency allows only mild media restrictions that can be challenged by editors in court.

Such a decree would probably serve to reopen what has been a long-running battle between the military and opposition journalists in Chilean courts. In the three years before the state of siege, Chilean journalists slowly were able to expand the limits of critical reporting by using the military's own 1980 constitution against them.

During 1983 and 1984, government authorities consistently attempted to close down magazines and radio stations, prohibit new ones, or impose censorship on those that existed. In a half dozen cases, they were defeated by editors who appealed to the Chilean Supreme Court.

Even an effort by government lawyers last year to prosecute opposition publications on national security grounds yielded no results. Meanwhile, several opposition journals expanded from narrow economic criticism of the government to extensive coverage of opposition activities .

"Every time they tried to box us in, we got out by using the courts," said Maria Olivia Monckeburg, an editor of the magazine Analisis. "Finally it was clear that they had had enough of us -- and we got the state of siege."