One year after Aquino killing, political fuse burns on

Something in the Philippines snapped when Benigno Aquino Jr. was assassinated at Manila airport a year ago. The country plunged into an economic crisis from which it has not yet shown any signs of recovery.

Equally important was the sea change in popular attitude to the regime. The government of President Ferdinand Marcos has become isolated, ignored as much as possible, and feared rather than respected by its people. It stays in power largely thanks to the armed forces, and to the inability of the opposition to present a convincing alternative.

The one real challenge to Mr. Marcos had been Mr. Aquino. The crudeness and arrogance of the killing were stunning. And the search for those responsible remains a political threat to Marcos.

Last Aug. 21, within seconds of getting off his plane after a three-year exile in the United States, Aquino was shot from behind at close range. The government claimed that Aquino's killer was Rolando Galman, a petty gangster allegedly hired by the Communist Party of the Philippines. But its story was riddled with discrepancies. Two examples:

* Aquino was shot from behind in a downward trajectory, pathologists said. Mr. Galman would have had difficulty doing this: he was shorter than Aquino.

* The government said Galman was hiding behind service steps leading from the plane's disembarkation tunnel to the tarmac. Yet the open-frame stairs gave no cover to anyone. And the plane was surrounded by an elite security unit.

After a first inquiry panel floundered in a sea of skepticism about its independence, a second board was appointed. Several witnesses told this panel that Aquino, under military escort, appeared to have been shot on the stairs: He had been carried, limp, down the last few steps and dropped on the tarmac. At least two also claimed that Galman was standing with a group of soldiers some distance in front of Aquino when the first shot rang out.

The inquiry commission is expected to make its results known on August 31.

Few people believed the government story. The most common conclusion among many Filipino was that the soldiers who escorted Aquino off the plane had killed him, on orders from very high up - close to the President, to say the least.

It is possible that the killing was linked in some way to a succession crisis. Marcos was incapacitated by illness when Aquino returned. Aquino's wife, Cory, says that her husband was convinced that Marcos was seriously ill, and that Aquino was racing against time to try to negotiate with Marcos while he was still in charge.

Many supporters and associates of Marcos also had their doubts. Soon after the assassination, for example, Gen. Hans M. Menzi, the publisher of Manila's biggest newspaper, the Bulletin Today, a former aide-de-camp to the President, and until his death last June an ardent admirer of Marcos, gave this correspondent and two colleagues his theory of the killing, pointing a finger at armed forces chief of staff, Gen. Fabian Ver. ''It was a stupid job, and Ver is stupid. It must have been him.''

General Ver is a relative of the President and - apart from Marcos's wife, Imelda - his closest aide. The skepticism extended to Manila's foreign allies. Speaking recently off the record to this correspondent, a Cabinet minister from one of the six-member Association of Southeast Asian Nations commented that Marcos could not afford a real investigation into the killing ''because it would get too close to him.''

The assassination crisis was a grievous shock to the Reagan administration. Washington's cherished belief that the Marcos government was nothing if not stable was shown to be illusory. The United States quickly distanced itself from Marcos, and has since been engaged in the delicate exercise of urging reforms on the government while avoiding friction over its strategically important military bases here.

The disappearance of confidence in the regime - at home and abroad, among elite and in the streets - has sorely hampered the government's efforts to pull itself out of deep economic crisis. The killing did not cause the crisis, but it aggravated it. The government claims that the political and economic uncertainty caused the exit of some $1 billion out of the country in the space of two weeks in early October after the killing.

These figures are now in doubt as the government was later discovered to have been exaggerating its foreign reserves by at least $600 million for much of 1983 , but the loss was definitely great. The Philippines now has a foreign debt of $ 25.6 billion. Inflation was unofficially estimated at 43 percent in the first half of this year, and 50,000 workers were laid off - double the figure for the same period last year.

To start getting out of this economic crisis, the government needs a $630 million loan from the International Monetary Fund (IMF). This would open the way to a $1.65 billion package of commercial loans - all of which will be used just to pay off debt arrears.

The government hoped to have the loans by the beginning of this year. The beginning of next year is now the most optimistic prediction. The IMF is uncomfortable about the amount of money which is now in circulation, pushing up prices. And its confidence in the government was shaken by the misstatement of foreign reserves.

The fact that the Filipino business elite has emerged as one of the most effective anti-Marcos groups must further weaken the IMF's confidence in the government.

The economy took another beating before the May 14 elections to the Batasang Pambansa (National Assembly). Financial analysts suspect that the government pumped more money into circulation, thereby keeping the economy looking healthy until after the elections.

The government still lost more seats than it expected: 61 out of 183. The opposition would probably have obtained more seats had it not been for apparently widespread fraud. The election was essentially a victory for the political center, and particularly for a group that did not contest the elections - the National Citizens' Movement for Free Elections, a largely middle-class watchdog group organized with the backing of the Roman Catholic Church and business.

But since then the center seems to have lost ground. The parliamentary opposition by and large is not particularly impressive. The Batasang's powers are limited: the President can still rule by decree under Amendment Six to the Constitution if he sees fit. The focus of political agitation has returned to the streets, where the underground Communist Party of the Philippines enjoys a distinct superiority.

Marcos has recently made much of the alleged growth of the communist guerrilla movement in the countryside. But it is in the cities that the communists have expanded over the last year.

In recent rallies designed to build up to a massive commemoration Aug. 21, supporters of the far left have shown themselves to be the better organizers and tacticians. At the moment they are in a fragile alliance with the moderates, led by Aquino's younger brother, Butz. Ultimately their aims are mutually contradictory. The moderates want a political normalization. The left would probably be quite happy with the reimposition of martial law; this would eliminate any role for the moderates, and further polarize Philippines politics.