Gen. Augusto Pinochet's specially outfitted 707 was halfway across the Pacific 11 days ago when he received word that his state visit to the Philippines, scheduled to begin less than 24 hours later, had been cancelled by President Ferdinand Marcos.

Marcos' explanation then was that he suddenly had "urgent" business outside Manila and therefore could not receive Pinochet.

It was not until four days later that Marcos offered a more plausible excuse, which no one here believes, that a plot had been uncovered to assassinate both Marcos and Pinochet during the visit.

The episode, humiliating for Pinochet, who had hoped to demonstrate with his visit to the Philippines that his international image had improved, led last week to the firing of Chile's capable and widely respected foreign minister, Hernan Cubillos, whom Pinochet held responsible for the fiasco.

Cubillos' firing, has led to widespread fears here that Pinochet has now abandoned a policy of greater internal liberalization, supported by Cubillos, for a return to an even more personalized and repressive dictatorship. The latter course is advocated by Pinochet's daughter, Lucia Pinochet de Garcia, and Gen. Juan Manuel Contreras Sepulveda, among others.

Contreras, the former head of Chile's secret police, was charged by a grand jury in Washington with ordering the 1977 assassination of Orlando Letelier, a leading figure in Chile's exile movement who served as Salvador Allende's ambassador to Washington before Allende's Marxist government was overthrown by the military here in 1973. Chile has refused to extradite Contreras.

"The fall of Cubillos is not an isolated episode," Que Pasa, a generally conservative and progovernment magazine once partly owned by Cubillos, said last week. "Rather, it conforms to a change in the political line followed by the president, a change which has been suggested since the end of 1979 and which now appears, even if not formulated in words, expressed irrefutably in acts which are . . . far more important."

The news that Pinochet's visit to the Philippines had been cancelled was transmitted from Santiago to Pinochet aboard his plane. The jet was then only an hour from landing in Fiji, the first official stop on what was to have been a 12-day tour of the South Pacific and Hong Kong.

Cubillos and other members of the official party, sitting in the jet's second cabin, did not learn anything was amiss until they landed in Fiji, where hundreds of egg-and tomato-throwing demonstrators were waiting to greet them with placards describing Pinochet as "South America's Hitler."

Pinochet had already decided to cut short the trip and return to Santiago as soon as possible, which he did on March 24.

Although El Mercurio, Santiago's influential morning newspaper, which Cubillos once headed, and Pincohet himself attempted to protray Marcos' move as an insult to Chile rather than to Pinochet personally, neither the government's opponenets nor its supporters accepted this view.

"Even another dictator like Marcos obviously had second thoughts about Pinochet," said one Chilean businessman supportive of the military government here. "Even in a small and remote island like Fiji, Pinochet was met by demonstrators throwing eggs and tomatoes. Can you imagine if he tried to go to Europe or, after Letelier, to the United States?"

Cubillos refused to accept responsibility for the Phillippines fiasco because he believed there was no way that it could have been predicted, or avoided, once Marcos made up his mind to cancel the visit at the last minute.

Last Friday, Pinochet appointed a career diplomat, Rene Rojas Saldames, to replace Cubilos. Although he is a civilian, Rojas' appointment was greeted here with less than widespread enthusiasm.

The decision to fire Cubillos has been interpreted in political circles here, including the opposition Christian Democrats, as part of the larger fight now going on around Pinochet. This is said to be a conflict between so-called soft-liners like Cubillos and hard-liners like Contreas, who are tryng to influence the military government, its economic policies and the increasingly urgent question of whether Pinochet will remain dictator for life or will begin a transition to civilian rule.

Alone among civilian ministers in Pinochet's Cabinet, Cubillos has an independent power base among the country's economic and social elite. This elite, which supported the 1973 coup, now badly wants to improve Chile's international image.

Cubillos, who recognized that only an end to the human rights abuses and other highly visible forms of repression used by the military would lead to an improvement of the regime's image, had been the architect of the country's new foreign policy after becoming foreign minister in April 1978.

He had persuaded Great Britian to send an ambassador here after years of frosty diplomatic relations and had improved ties with other Western European nations. Cubillos had also managed to avoid a serious rupture with the United States over the Letelier affair and had conceived of the "opening to the Pacific," which was to have included state visits by Pinochet this year to the Phillippines, Japan and China.

But Cubillos could not overcome the image of Pinochet as a ruthless dictator whose international reputation is so bad that hardly any country is willing to receive him.

In the maneuvering around Pincohet, soft-liners like Cubillos have pressed to maintain the free-market economic policy followed by the government since 1974 while beginning the transition to some form of civilian rule.

Hard-liners advocate a more socially oriented, populist economic policy to balance a firm hold on power by Pinochet and the military for at least another 10 years.

Pinochet has moved erratically between the two groups over the past year, as Que Pasa pointed out last week, so far maintaining the free-market economic policies but recently clamping down again on dissenters and press freedom after a year of increasing tolerance.

It is in this context that the firing of Cubillos was seen as a victory for the hard-liners.