The acquittal today of all 26 defendants accused in the slaying of Philippine opposition leader Benigno Aquino will be widely perceived to have destroyed the few remaining shreds of credibility clinging to the Philippine judicial system, a supposedly independent one modeled on that of the United States.

Not only is the decision certain to undermine public confidence in the judiciary, but it could be seen by many as the death knell for justice under President Ferdinand Marcos.

Marcos won in the strictest and narrowest interpretation because the verdict exonerated, as expected, his closest and most loyal supporter, armed forces chief of staff Gen. Fabian C. Ver. But in a larger sense, this triumph may turn out to be a superficial and temporary one.

Outside the walls of the Malacanang presidential palace, the verdict seems certain to be widely viewed as yet another radicalizing element in the country's political turmoil; one more argument that no justice, no peaceful change, no reforms of any consequence are possible while Marcos remains in power.

The long-awaited verdict of a three-judge panel in the Philippines' most celebrated murder case upheld what Marcos had said from the beginning about the assassination of his political arch rival at the Manila International Airport on Aug. 21, 1983. That version, so widely disbelieved that not even loyal Marcos supporters take it seriously in private, is that Aquino was shot by Rolando Galman, a small-time hood allegedly hired by Communist rebels.

In the court of Philippine public opinion, the accepted version has long been what an official fact-finding board concluded last year: that Aquino was killed by a soldier in a military plot in which Galman, set up to take the blame, was also gunned down at the scene.

The broader implications of the verdict are also likely to reinforce one of the main tenets of Communist rebels waging a guerrilla war in the countryside. They will use the verdict as one more example in their rhetoric that justice is impossible with Marcos in power. In fact, independent efforts to trace the causes of the growing insurgency have found that injustice, rather than poverty, ranks highest among antigovernment grievances. Many Filipinos in rural areas now look to the guerrillas of the New People's Army to provide local justice.

The verdict also seems certain to become an issue in the upcoming presidential election campaign. Marcos, 68, who has been in power for 20 years, has called for an early presidential election in February, more than a year before his current six-year term expires, to seek a "new mandate."

Currently at the forefront of potential challengers to Marcos are Corazon Aquino, the 52-year-old widow of the slain opposition leader, and Salvador Laurel, who heads the United Nationalist Democratic Organization.

Besides becoming a campaign issue, the verdict could have political impact on the race in another sense. It may push moderates toward the leftist view that, like justice, a fair election is impossible under Marcos when his highest personal interests are at stake; that he will stop at nothing to prevent a defeat. Such an argument could fuel what appears to be an emerging boycott movement by leftists who denounce the scheduled Feb. 7 presidential election as a "U.S. imperialist ploy" to keep Marcos in power while sprucing up his image.

The howls of protest from political moderates that greeted today's verdict also illustrate the failure of Marcos' apparent strategy to bury the assassination in a morass of protracted, legal proceedings.

More than two years after the shooting, the killing of Aquino as he was returning home from three years of self-imposed exile in the United States is an issue that refuses to go away. Far from settling the case, the acquittal of all 25 military men and one civilian undoubtedly will fuel demands for a new trial in a post-Marcos era.

A group of prominent Filipinos have petitioned the Philippine Supreme Court to declare a mistrial, alleging that the trial court was biased in favor of the defendants, but the request was turned down last Thursday.

The trial court also came under criticism for allegedly being a tool of Marcos. Called the Sandigan Bayan, the court was established by a 1978 presidential decree while Marcos ruled the country under martial law. All its judges are Marcos appointees. In fact, shortly before the fact-finding board investigating the Aquino assassination issued reports last year implicating the military, Marcos appointed three new judges to the court to bring it up to its full complement of nine.

The head of the three-judge panel trying the case, Justice Manuel Pamaran, insisted nevertheless that the court was independent. But what followed was a verdict so beholden to Marcos that it even borrowed his arguments citing the assassination of president John F. Kennedy and a reported attempt against his wife, Imelda Marcos, as examples of security lapses.

For many Filipinos, the verdict simply flies in the face of the facts. Certainly, that is the view of the person considered most knowledgeable about the case, Andres Narvasa, a respected university law school dean who served as the fact-finding board's chief counsel.

The most compelling evidence of a military plot, Narvasa said in a recent interview, was a chronology he put together using still photographs taken by journalists, television news videotape and audio recordings of the events before, during and after the assassination of Aquino. The chronology was largely ignored by the defense in the Ver trial, and today's verdict dismissed it as irrelevant.

According to Narvasa and other lawyers, it represents hard evidence that the assassination simply could not have happened the way the military witnesses in the case said it did. While the killing of Aquino was not recorded on film, the sounds of it were recorded on tape.

What the tapes and photographs record is this: military men boarding Aquino's plane and escorting him through its door to a passenger tube; a guard wheeling and blocking cameramen as Aquino is taken down a service stairway; shouts of "Here he comes" and "I'll do it" followed by one shot, two more shots, then a volley of gunfire; images of a soldier pumping automatic rifle fire into the prostrate body of Galman in an apparent attempt to finish him off; and other soldiers roughly picking Aquino off the tarmac and shoving him face-down into a van before speeding away.

According to today's verdict, Galman somehow knew which plane was carrying Aquino and just where he would be escorted off. Galman, waiting on the tarmac, darted behind Aquino and shot him once in the back of the head.

According to a reenactment by the fact-finding board that was compared to the video and audio tapes, Aquino did not have time to exit the plane and reach the bottom of the service stairs before the first shot, the one that killed him, rang out.