A group of prominent Filipinos is preparing to petition the Philippine Supreme Court to declare a mistrial in the Benigno Aquino murder case, arguing that those they believe to be responsible for the killing of the opposition leader in 1983 are on the verge of escaping justice.

According to lawyers involved in drafting the petition, the basis for the mistrial argument is that government prosecutors in the case against 25 military men and one civilian have not been trying very hard to win.

Among what one lawyer called "the horrid lapses of the prosecution" were a failure to ask for reconsideration of a Supreme Court ruling that threw out key evidence, a refusal to call rebuttal witnesses and rejection of affidavits and offers to testify from six U.S. servicemen concerning the mysterious scrambling of Philippine Air Force fighters before Aquino's arrival at the Manila International Airport.

"It all means there was no attempt to prosecute," said lawyer Bienvenido Tan, one of the petitioners and a former counsel of an official fact-finding board that indicted the 26 suspects.

Another lawyer who is close to Marcos' opposition, Rene Saguisag, said the prosecution's handling of the case "amounted to a lack of due process."

More than two years after the assassination of Aquino as he was being escorted from an airliner by military guards, the trial of those accused of plotting, carrying out and covering up his murder is dragging to a conclusion.

A three-judge panel began deliberations last week and has 90 days to reach a verdict. Awaiting the court's decision are the armed forces chief of staff, Gen. Fabian Ver, two other generals, 22 military officers and enlisted men and a civilian businessman.

Many Filipinos appear to have accepted the conclusion -- reached by the official fact-finding board and several independent panels that reported before the trial began -- that the political arch-rival of President Ferdinand Marcos was killed by the military men who took him into custody seconds after his Aug. 21, 1983, homecoming from three years of self-imposed exile in the United States.

The military claims that Rolando Galman, 33, a small-time criminal with a long police record, shot Aquino on behalf of Communist rebels before being gunned down himself by military guards assigned to protect the opposition leader.

This claim was endorsed and promoted by Marcos, although he later tried to distance himself from it when the fact-finding board he appointed concluded in October 1984, after a year-long inquiry, that Aquino was the victim of a military plot and that Galman was set up to take the blame.

The board turned over its evidence last year to a government ombudsman empowered by Marcos to take the case. The 26 defendants implicated by the board in a majority report then went on trial in a special court normally used to try low-level government officials on corruption charges.

With the ombudsman's office prosecuting, the case did not go beyond the fact-finding board's evidence except for the appearance of an elusive witness, Rebecca Quijano, known as "the crying lady." She testified that she saw a soldier shoot Aquino in the back of the head as he was being taken down a service stairway to the airport tarmac.

As a result of her testimony, the prosecution last month named one of Aquino's escorts, Philippine Constabulary soldier Rogelio Moreno, as the opposition leader's assassin.

Aside from Quijano's appearance, much of the trial seemed to go in favor of the defense.

Then, in August, the Supreme Court upheld a trial court ruling that the testimony given to the fact-finding board by Gen. Ver and seven other military men accused as "accessories" could not be used against them, even though they had volunteered what the board found to be false and misleading statements. Shortly after the ruling, the deputy prosecutor, Manuel Herrera, stopped appearing in court and directed all inquiries to his boss, Justice Bernardo Fernandez.

According to legal sources, the two had disagreed on Herrera's intention to call at least a dozen rebuttal witnesses, which was overruled by Fernandez.

The U.S. Embassy in Manila also complained publicly about the prosecution's performance when Fernandez rejected an offer to make available six U.S. servicemen to testify on the scrambling of two Philippine jets about the time Aquino's flight was arriving.

According to a Philippine intelligence source, the scramble was not aimed at diverting Aquino's flight but at intercepting a light private plane to verify that he was not on board. Diplomats said the U.S. airmen's testimony could have pointed to a wider conspiracy in the Aquino case and implicated high-ranking Philippine officers.

There is now widespread expectation that Ver, a close aide of Marcos, will be acquitted, since the court threw out the evidence as directed by the Supreme Court.

It was in response to the doubts that justice would be done that a group of prominent lawyers, retired judges, businessmen and other professionals decided to petition for a mistrial. They plan to file their request this month, lawyers said.

In view of what they see as the likely prospect that the Supreme Court will rule against them, the petitioners make it clear that they are pursuing their case with a view to Marcos' succession.

"People are talking of a new trial under the next regime," said opposition lawyer Saguisag.

Since the petitioners began drafting their arguments, Marcos has called for an early presidential election, at first saying the date should be Jan. 17. The judges have until Jan. 23 to issue their verdict.