The trial of four men accused in the slayings of two Navajo tribal policemen began Monday with an assistant U.S. attorney saying witnesses will testify that one of the defendants was seen holding the gun of one of the victims.

Assistant U.S. Attorney Stewart Walz told the jury that witnesses can place the gun of Officer Roy Lee Stanley in the hand of one of the defendants, Vinton Bedonie.But defense lawyer Walter Bugden, representing Marques Atene, declared, during his opening statement: "They haven't solved this crime. These defendants are not guilty. They've arrested the wrong men."

The trial of four defendants - Bedonie, Thomas Cly, Ben Atene Jr. and Marques Atene - is being heard before U.S. District Judge J. Thomas Greene. The defendants are accused of first-degree murder of Stanley and Officer Andy Begay, both Navajo tribal policemen.

Walz said the officers were killed after Stanley came upon a party at a crossroads on the reservation the night of Dec. 4, 1987. After a fight, Stanley was disarmed and taken behind his truck, where he was shot, Walz said. Stanley apparently had a chance to use his police radio, and Begay drove to the scene afterwards.

Walz said witness Boyd Atene will testify that the Bedonie forced the witness to sit in the driver's side of the truck.

He will testify that Stanley was shot and that when Begay arrived, Bedonie leveled the gun at Begay, took him behind the truck, and ashot was fired, Walz said.

The trucks were then driven to Copper Canyon. Walz said Boyd Atene will testify that defendant Thomas Cly did most of the dousing of the victims with gasoline. They were then set on fire.

Walz said the bodies were discovered in the truck the morning of Dec. 5, 1987, by a man and his son who left Kayenta, Ariz., to go fishing in Lake Powell. They were driving through Copper Canyon when they came upon the two burned-out GMC Suburbans, Walz said.

"In there (Begay's truck) they found the charred remains of two individuals," he said. "These were later identified as the bodies of Stanley and Begay."

Walz said the fire was so fierce that the bodies only weighed 21 and 29 pounds. He said an autopsy showed they died in the fire.

A medical examiner said that "he found a slug or fragment of a bullet under Andy Begay's body," Walz said. The prosecutor outlined the numerous changes in testimony by some witnesses in this case. One of these, he said, is Raymond Fatt, who will tell the jury some of what happened at the bonfire, which he said he left in a hurry after the fight started.

"Ray Fatt last Monday, in another matter relative to this case, said he didn't go to the bonfire," Walz said. He said the latest change will be explained by Fatt testifying he was afraid and lied.

The defense attorneys then began their opening statements. They were expected to stress the fact that guilt must be proven beyond a reasonable doubt. Also they have indicated that they may try to blame non-Indians.