Washington Post Foreign Service Chile's right-wing military junta yesterday fired the only member of the four-man ruling body who had dared to publicly oppose the policies of President Augusto Pinochet.

The dismissal of Gen. Gustavo Leigh from his positions both as commander in chief of the air force and as a member of the junta was the first change in the granite-like unity of the government that has ruled Chile since the military overthrew Marxist president Salvador Allende in a 1973 coup.

According to a government communique, Leigh was fired because of his "repeated neglect of the principles and postulates that inspired" the coup.

The communique said that Air Force Gen. Fernando Mathei, former minister of health, has replaced Leigh in both posts.

Long at odds with Pinochet, who is also a junta member as commander of the army, Leigh in recent months had openly opposed the president's increasingly personal dictatorial rule and had called for a speedup in Pinochet's 10-year timetable for return to partial democratic rule.

The firing, in which the government said the other three junta members concurred, is viewed as a victory for the hardline faction within the Pinochet government.

Leigh, 57, was originally considered the most conservative member of the junta, which includes the heads of the three military services and the national police.

Within hours after the Sept. 22, 1973 coup, Leigh was quoted as saying that the junta's job was to "extirpate the Marxist cancer" from Chile. Human rights organizations allege that the junta subsequently engaged in the secret imprisonment and murder of thousands of Communist leaders and suspected sympathizers.

Early this year, however, aides close to Leigh said that he had become increasingly disenchanted with Pinochet because of the president's apparent desire to increase and perpetuate a "totalitarian" government with himself as director.

Authoritative Chilean sources said that Leigh's decision to break openly with Pinochet came last January, when the president unilaterally called for a national referendum on support for his leadership. Leigh called the referendum, which Pinochet won by a large margin, the "biggest mockery in Chile's democratic history" and said it would fool none of Chile's international critics.

At that point, the sources said, Leigh met with top air force generals and received a unanimous vote of support for a program of opposition to Pinochet. That program began in March with a series of speeches critical of the government's economic and political programs.

The friction within the junta came to a head last week following publication in Chile of an interview Leigh gave to an Italian newspaper during a recent trip to Europe.

In the interview, Leigh called for a firm timetable cutting in half Pinochet's vaguely outlined 10-year plan for return to democracy. He also emphasized the importance of reviving civilian political parties, which are now prohibited under Chilean law.

At the time of the referendum last January. Leigh reportedly was so incensed over Pinochet's action that he wrote a private letter of protest to the president, and his office leaked a copy to the Christian Democrats, the largest political party.

Leigh also objected to the government's handling of the U.S. investigation of the 1976 Washington assassination of exiled Chilean diplomat Orlando Letelier.

According to informed sources, Leigh last year favored an early response to a number of unofficial U.S. requests for assistance on the case which the government had ignored. That lack of cooperation eventually led to a serious diplomatic row between the two countries earlier this year.

The sources said Leigh opposed Pinochet's attitude of blaming "international communist conspiracies" for Chile's problems and feared a total economic and weapons boycott if the government did not become mere pragmatic.

Mathei, Leigh's replacement, is ranked number 10 among the Air Force's 16 generals. The fact that he was named for the top job indicates that all those above him were retired.

According, to wire reports, the streets of Santiago, Chile's capital, were quiet yesterday as news of Leigh's removal spread. A crowd of about 200 gathered in front of the Air Force Ministry, however, and army troops were stationed on the roof of the building.