A jury began deliberating yesterday the case of Michael G. Simoneau, accused in the slaying of a homosexual at the Iwo Jima Memorial, after hearing Simoneau's attorney declare: "This man is guilty. There is no question about that. He's here to take his punishment."

The question placed before the Arlington Circuit Court jury was the nature of the offense and therefore what the punishment should be.

The defense attorney, John A. Keats, argued that Simoneau should be convicted of manslaughter (killing without malice, committed in the heat of passion or combat) for which the maximum punishment is 10 years.

The prosecution asked the jury for a first-degree murder conviction for Simoneau's role in the slaying of Ronald J. Pettine, a former aide to Rep. Morris K. Udall whose nude and battered body was found at the memorial Oct. 2, 1976.

First-degree murder is punishable by a prison term up to life or by electrocution, but the prosecution said it was not seeking a death sentence.

Simponeau, 17, who is being tried as an adult testified Wednesday that his encounter with Pettine occured on his 16th birthday when he and two friends, Charles A. Bamman, 21, and Alan J. Arnone, 22, went to the Iwo Jima Memorial in Arlington - a well-known meeting place for homosexuals, to "harass and humiliate queers." He said he had not intended to kill or rob anyone.

Simoneau denied abusing Pettine's sexual organ or dragging his body, as several witnesses testified Simoneau told them he had done. Both Bamman and Arnone are scheduled to stand trial later on murder charges in Pettine's death.

Keats argued that Simoneau and his friends were preoccupied with a "macho syndrome" and felt that homosexuals' activities at the memorial honoring the U.S. Marines desecrated it. Keats siad Simoneau's brother is a Marine.

Elizabeth Pettine, the dead man's widow, testified at the start of the trial Monday she had known "for about three years" that her husband was a homosexual and that he mixed publicly with homosexuals.

Two homosexuals testified they engaged in sexual acts with Pettine in woods near the memorial the night of the slaying but were interrupted when two men entered the woods. Pettine walked toward the men, they testified, and suddenly the men were on top of him, beating him.

They said Pettine screamed, "help me, help me. Tthey're trying to kill me," and that they ran away.

Simoneau, the only defense witness, testified he had intended to "smack around a few queers." He said Bamman and Arnone entered the memorials wooded area and a man approached him. The man, identified later a Pettine, asked him for a sexual favor, Simoneau said.

"I was pretty well drunk and it got me plain mad," the youth said. "I pushed him. He pushed me back. We both hit the ground."

Simoneau said Bamman and Arnone then "came out of the woods and went crazy on him." He said he watched as Arnone kicked Pettine and Bamman hit him with a tree limb.

Assistant Commonwealth's Attorney Kenneth Melson said in his closing argument that "no one should encourage what goes on down at the Iwo Jima, nor should anyone encourage tha activities of Mr. Simoneau. Mr. Simoneau is on trial here, not Mr. Pettine or what he was doing ."

George Berklacy, a U.S. Park Service spokesman, said yesterday that since the slaying, underbush around the memorial has been cleared and he knows of no arrests for homosexual activity since then. He added that two complaints have been made since then that homosexuals had propositioned others near the memorial.