Michael G. Simoneau, 17, accused of murder in connection with the October 1976 beating death of a former aide to Rep. Morris K. Udall (D-Ariz.), told three friends hours after the slaying that he "may have killed somebody," the friends testified yesterday.

Simoneau also told them, they testified at his trial in Arlington Circuit Court, that he and two other friends had "beat up a fag," abused the man's sexual organs and left him near the Iwo Jima memorial in Arlingotn, a known meeting place for homosexuals.

The man that Simoneau and two other men are accused of murdering at the memorial is Ronald J. Pettine, who besides being a former Udall aide was a former deputy secretary of state in Pennsylvania an d a husband and father of two children. Pettine's wife testified Monday that he was also a homosexual.

The testimony came on the second day of Simoneau's trial as an adult on murder and robbery charges in connection with Pettine's death on Oct. 2, 1976. Charles A. Bamman, 21, and Alan J. Arnone, 22, were also indicted on murder and robbery charges in the slaying and are scheduled to stand trial later this year.

The prosecution contends that Simoneau and the two others wanted to rob a homosexual, then kill him and Simoneau was a leader in the undertaking.

John A. Keats , Simoneau's attorney, contends that his client should be found guilty of manslaughter or a lesser charge rather than murder because Simoneau didn't strike Pettine, who Keats said was beaten to death with a tree limb by Bamman. The attorney also argues that the three went to the memorial to "find a homosexual and rough him up, humiliate him . . ." rather than kill him.

Simoneau's friends, called yesterday b y the prosecution, testified that Simoneau told them Bamman struck Pettine with the tree limb. They also testified that Arnone, known as "Big Al," is only between 3 and 3 1/2 feet tall.

One of the witnesses, Mark Posey of Arlington, said Simoneau came to his home the day after the slaying and "told him and Chuck (Bamman) and Al(Arnone) went down to Iwo Jima and beat up a faggot. They just said they beat him up pretty good, they didn't know if he was dead."

"They kicked him, hit him, ripped his clothes of f." Posey continued. "Chucky (Bamman) hit him with a stick . . ."

Posey said Simoneau telephoned him later and "said he may have killed him, he wasn't sure . . . I told him to keep his cool, not say nothing about it."

Deputy Medical Examiner James C. Beyer testified yesterday Pettine died from a blow to the skull and that he had numerous bruises and cuts on his body, including his sexual organs.