When is a trial not a trial? And when is a trial over? In the Philippines, the answer seems to be that trials at least in his military courts, are whatever President Ferdinand Marcos makes them.

The Philippine politician's hand traditionally has been faster than the outsider's eye. Nevertheless it is a tribute to what Marcos has achieved in five years of martial law dictatorship that even death sentences appear to have become gambits to be played. That is political hardball, Philippine style.

For more than 10 years, Marcos has been in political combat with former senator, now condemned prisoner, Benigno Aquino. When Aquino first ran for the senate at the age of 34 in 1967, he remarked to a reporter: "President Marcos is pulling out all the stops against me." Aquino won that election, but there were several sets of organ pipes Marcos hadn't touched then.

Now, Aquino has been in prison since September 1972 when Marcos declared martial law, and two weeks ago a military court sentenced Aquino to be shot by a firing squad on charges of subversion, murder and illegal possession of firearms.

But hold everything. Four days after Aquino was sentenced, Marcos ordered the case reopened in order to hear further evidence from the defendant. At first glance, the president appeared to be bending over backward to be fair. However, his gestures ignores what has always been Aquino's central protest and appeal - that he cannot receive a fair trial in a military court whose strings Marcos pulls and that he wants to be tried in civilian court.

Aquino has refused to defend himself before the military court so that more time, post-sentencing, is not what he wants, and Marcos knows it.

When Aquino was arrested at the Manila Hilton Hotel on the eve of the martial law, he was the president's most likely challenger in the scheduled 1973 election and was given a good chance of winning. Although martial law canceled the election, it has not ended the two men's rivalry, but made it a curious test of wills between a ruler with unlimited power and a man in solitary confinement.

As he has at each of his infrequent opportunities to speak during court proceedings against him. Aquino greeted his sentence by aiming his words over the court's head. "If Marcos believes I'm guilty, I want to be shot tomorrow."

Aquino denounced an earlier court action in flamboyant terms reminiscent of his campaign oratory and concluded by saying that his actions express "my utter contempt for the man who has brought me so much suffering and [brought] so much injustice to our people."

Marcos has responded to Aquino's rhetoric with some embarrassment not reduced by the Carter administration's concern about human rights. Congress cut military aid to the Philippines this year out of concern about human-rights violations. U.S.-Philippine negotiations have resumed on the future of U.S. bases there for which Marcos wants large rents.

When Henry Kamm of The New York Times asked to interview Aquino in prison early this year, Marcos replied: "You're going to build him up again." The president said he would grant the interview if Kamm promised not to write about Aquino. "But if you are going to pit me against Aquino and quote him more than you quote me, then we're both going to be in trouble."

In one of the dazzling twists of the rivalry that has seen Aquino declare a fast to the death only to call if off after 40 days when Marcos made clear the prisoner would be force fed if necessary, Marcos fetched Aquino from jail to the Presidential Palace last June for a face-to-face meeting.

Aquino later told the court that Marcos reminded him of a messenger who warned him in 1973 that martial law was about to be imposed. "Well, I really wanted you to run away," Aquino quoted Marcos as saying.

Only Aquino's stubbornness apparently prevents him from running away now, from making a deal accepting exile in exchange for some sort of admission. Aquino does not consider himself guilty and has so far refused any deal.

The substance of the charges against Aquino are blurred and almost disapper behind the postures of the participants. Aquino admits he had weapons that were illegal, but points out that before martial law every other wealthy Filipino did too. He also admits he had contacts with members of the Communist New People's Army (NPA), but denies he stared their beliefs and says he only wanted to hear their views. He is innocent of murder, he says.

The main thrust of his protest in his private meeting with Marcos, as in all his public statements, is that he should be tried by a civilian court.

In Manila and among U.S. observers, it is expected that the death sentence was a gambit to increase the pressure on Aquino, but by no means the last twist in the case. Marcos might even consider a form of pardon for Aquino, which would enhance the president's credentials as a respecter of human rights, unless one remembers how closely he controls the military court from whose sentence Aquino would be pardoned.

Before martial law was imposed, a series of bombs exploded in Manila office buildings at night, and in one of Aquino's last speeches to the senate, he accused Marcos of deliberately creating a climate of violence to justify martial law. His charge is not proven. The bombings have not been explained.