The Supreme Court of the Philippines today barred a trial court from handing down its verdict in the Benigno Aquino murder trial until the high court rules on a petition to declare a mistrial in the case.

The restraining order came a day before the verdict in the case against Armed Forces Chief of Staff Fabian Ver and 25 others was to be rendered. It was issued after the court heard arguments yesterday from lawyers of the petitioners who said that the trial court's integrity was being questioned and the mistrial petition thus should be heard first.

No date has been set for the next session of the hearing on the petition, which was filed by 31 prominent Filipinos and accuses the three-judge court and the prosecution of bias in favor of Ver and the 25 other accused and charges that the prosecution failed to present all the evidence in the 1983 airport assassination of the prominent opposition leader.

Lawyers for the accused had asked the high court to let the trial court give its verdict, saying the accused had endured two years of legal proceedings including the trial and an official inquiry.

The restraining order, by a vote of 9 to 2, was the last official act of Chief Justice Felix Makasiar, who retires Wednesday at the mandatory age of 70. President Ferdinand Marcos today announced the appointment of another ally, Justice Ramon C. Aquino, 68, as the new chief justice. Both men voted against the restraining order.

Aquino's appointment marked the second bypassing of Associate Justice Claudio Teehankee, the most senior justice on the court, who is known to be independent and has issued rulings against the Marcos government. He is no relation to Benigno Aquino. Teehankee was bypassed two months ago when the post went to Makasiar.

Ver, the highest ranking defendant in the trial and a Marcos confidant, is expected to be acquitted. There is no evidence against him since the Supreme Court threw out the main body of evidence against him that consisted largely of his own testimony before the official fact-finding board last year.

The high court ruled in favor of Ver and seven other accused, including Manila's police chief Maj. Gen. Prospero Olivas. They were charged as accessories on the lesser charge of covering up the crime. Seventeen soldiers were charged as principals and the lone civilian was charged as an accomplice.

Observers of the trial say the highest ranking officer likely to be found guilty could be Brig. Gen. Luther Custodio -- who was in charge of the airport security unit when Aquino was slain -- together with six of his men.

They also were charged with the murder of Rolando Galman, who the military said shot Aquino, but who the official inquiry said was set up. Galman was killed on the spot by the soldiers.

The general thinking here is that the verdict will follow closely the dissenting opinion of the official inquiry headed by Corazon Agrava, which indicted the seven most immediately involved in security arrangements at the airport for Aquino.

The majority opinion indicted all 26 men as part of a wide conspiracy.

With campaigning for the country's snap presidential election set to begin next month, some analysts think that Marcos feels confident that the Aquino trial verdict and petition drive will have little impact on the election.

The largest opposition coalition, UNIDO, found in a September survey that the Aquino murder ranked No. 4 in issues Filipinos hold against Marcos, after the economy, the Communist insurgency and official graft and corruption.

Internationally, however, concern over the trial, the possible reinstatement of Ver as chief of staff as well as the other issues noted in the survey is increasing. President Reagan recently dispatched Sen. Paul Laxalt to convey U.S. concerns in a number of areas to Marcos, and in Congress legislators have begun to pressure him for major reforms.