Judges conducting the trial of 26 persons charged in connection with the 1983 assassination of Philippine opposition leader Benigno Aquino Jr. ruled today that earlier testimony given by armed forces Chief of Staff Fabian Ver and seven other officers cannot be used against them.

Ver and the seven other officers are charged as "accessories" in a cover-up of the murder. The court cited the constitutional right against self-incrimination as the basis for its ruling.

The unanimous ruling by the three judges hearing the case at Manila's special civilian court, the Sandigan Bayan, was seen here as a step toward acquittal of Ver and possibly others accused in the Philippines' most celebrated murder trial.

Marcos relieved Ver temporarily last year when a majority report of the fact-finding board investigating the assassination implicated the general in the murder. Marcos has said he intends to keep his "word of honor" to reinstate Ver as armed forces chief of staff if he is acquitted in the current trial.

But Reagan administration officials and some U.S. congressmen have made it clear to Marcos that they would consider Ver's reinstatement inimical to efforts to promote major reforms in the Philippine armed forces. Washington considers the reforms essential to help counter a growing Communist insurgency and clearly places greater stock in Ver's replacement, acting chief of staff Lt. Gen. Fidel Ramos.

On trial for the murders of Aquino and Rolando Galman, a small-time gangster blamed by the military for the assassination, are 25 military men and one civilian. Seventeen of the military defendants, including one general, are charged as principals in the case, and the civilian is charged as an accomplice.

Government prosecutors have pinned their case against Ver and the other alleged accessories on an October 1984 report by four of the five members of the fact-finding board that investigated the assassination for nearly a year. The report includes allegedly self-incriminating testimony, documents and other evidence produced in response to subpoenas from the fact-finding board. The eight are essentially accused of having lied to the fact-finding board as part of a military coverup after the assassination of Aquino, the political archrival of President Ferdinand Marcos.

In today's ruling, the judges said they were accepting two fact-finding board reports and supporting exhibits as evidence, except for the portions held to be self-incriminating. Lawyers for the other 18 defendants in the case had argued for rejection of all of the reports and exhibits.

Gen. Ver's lawyer, Antonio Coronel, said his next move would be to "file a motion to dismiss the charges" against his client. He has pointed out that none of the 79 prosecution witnesses called since the trial began three months ago has testified against Ver.

However, lawyers with links to the prosecution said further evidence or testimony against Ver might be introduced. But there was no indication what that might be, since the prosecution has already said it would call no more witnesses and has all but rested its case.

Asked if the ruling meant Ver would be acquitted, one of the judges in the trial, Augusto Amores, told an Associated Press reporter, "No, we have to assess the evidence and see if there's evidence against Gen. Ver." But he conceded that the ruling was "definitely" a blow to the prosecution, and possibly fatal to its case against Ver.

Ver, 64, the Philippines' most powerful military officer and a longtime close confidant of President Marcos, was accused in the majority report of having lied to or misled the board regarding efforts to track Aquino's movements as he headed back to Manila after three years of self-exile in the United States.

The report said, for example, that Ver during testimony produced a medical contingency plan that he said was part of security precautions in effect for Aquino's arrival from exile, although no such plan existed then. A dissenting report by the board's chairman specifically absolved Ver.