A group of prominent Filipinos petitioned the Supreme Court today to declare a mistrial in the proceedings against armed forces chief of staff Gen. Fabian Ver and 25 others charged in the assassination of opposition leader Benigno Aquino Jr. The petition charged that the prosecution arranged the trial "to favor the accused and ensure" the acquittal of the 26.

In another development today, President Ferdinand Marcos submitted his postdated resignation as president to pave the way for a snap presidential election on Jan. 17.

In a letter to the speaker of the National Assembly, Marcos, 68, said he was seeking a fresh mandate for another six-year term. But he made clear that he would "irrevocably" vacate the presidency "only when the election is held and after the winner is proclaimed and qualified as president by taking his oath of office 10 days after his proclamation."

In their petition to the high court, the 31 signatories, including three retired Supreme Court justices, accused both the trial court and the prosecution in the trial of Ver and the other 25 of failing to "serve the interest of the people" through "manifest partiality and injudicious and irregular conduct."

The petition also demanded that the court be stopped from handing down a verdict -- which is expected soon -- because the trial was "designed and deliberately arranged by the prosecution to favor the accused and ensure their acquittal."

The petitioners also included businessmen, human rights lawyers, opposition politicians and the mother and son of Rolando Galman, the man found by an official fact-finding board to have been set up to take the blame for Aquino's assassination.

The fact-finding board concluded that the August 1983 assassination of Aquino was a military conspiracy, and it indicted one civilian and 25 military men, including Ver.

Lawyer Bienvenido Tan, who acted as the fact-finding board's public coordinator, said he had doubts about its prospects before the Supreme Court, where, he said, Marcos' loyalists outnumber independent justices. But he said, "We have to put this on record . . . so that at some future date when Mr. Marcos sees the light or in the next administration, there will be a chance to reopen the case."

Marcos' resignation letter today was attached to a bill drafted by the Cabinet and submitted to the assembly by Prime Minister Cesar Virata. The bill lays out the ground rules for the elections for president and vice president. It was referred immediately to a parliamentary committee and is expected to be passed by next week.

The snap election plan has been criticized even by some of his own party colleagues. Maverick back-bencher Arturo Tolentino, whom Marcos fired as foreign minister for his outspoken views, said the "resignation is worthless, whether he [Marcos] wins or loses."

Within opposition ranks, where Marcos' resignation maneuvering is considered unconstitutional, signs of a trade-off began to emerge today and back-room negotiations with the ruling party began as soon as the bill was submitted.

Four opposition leaders today endorsed Corazon Aquino, widow of the slain opposition leader, as their candidate in the scheduled elections. She has said that she would only run if all opposition factions support her and if they can collect one million signatures supporting her candidacy. Eight other opposition leaders have endorsed Salvador Laurel, a former Marcos ally.