Superior Court jury here found two men guilty this afternoon of first-degree murder and conspiracy in the bombing death of investigative reporter Don Bolles.

The jury convicted Phoenix contractor Max Dunlap and plumber James Robison of all charges against them in the sixth day of deliberations.

Judge Howard Thompson set sentencing for Dec. 6. The two men could receive the death penalty. Attorneys for both said they plan to appeal.

Dunlap and Robison showed no emotion as the verdicts were read, but Dunlap family members gave a collective gasp and some wept openly.

Bolles, 47, the father of seven and a prize-winning reporter for the Arizona Republic, was fatally injured June 2, 1976, when a bomb blew up under his car near a hotel when he was investigating alleged fraudulent land deals involving Arizona politicians.

Until January, John Harvey Adamson, 33, a sometimes greyhound racer and minor figure in Phoenix organized crime circles, alone faced a first-degree murder charge. But he was allowed to plead guilty to second degree murder on Jan. 15 after his attorneys negotiated with state prosecutors.

Dunlop, 46, and Robison, 55, were arrested by police the same day that Adamson agreed to testify against them.

The trial of Dunlap and Robison, delayed repeatedly by defense motions, started July 11 with jury selection. Opening arguments began Sept. 2.

Six days later, Adamson took the stand to answer questions from chief prosecutor William Schafer III.

Adamson said Dunlap hired him to kill three men - Bolles, Arizona Attorney General Bruce Babbitt, and Al Lizanetz, a local public relations man. The ""package price," Adamson said, was $50,000.

Adamson quoted Dunlap as saying the three were marked for revenge because they had attacked the reputation or business interests of Kemper Marley Sr., a wealthy Arizona liquor wholesaler who Dunlap said "raised me up almost like a son."

The name of Marley, 71, surfaced frequently in the trial. He has been charged with no time in connection with the Bolles murder.

Adamson, who wore dark sunglasses throughout the trial, testified that Bolles was targeted because his newspaper articles critical f Marley cost the aging multimillionaire a seat on the powerful Arizona Racing Commission.

Adamson testified that he recruited Robinson, a personal friend, to help him carry out the murder with a remote-control dynamite bomb.

He said he lured the reporter to Phoenix's Hotel Claredon with a promise of information on a land swindle involving prominent Arizona politicians. He attached the explosive to Bolles' car while the reporter was inside the hotel, and Robinson detonated it. Adamson testified.

Seven days later, Adamson said, Dunlap gave him "about $6,000 in a manila evelope" and offered to help his wife and child with living expenses.

Dunlap acknowledged to police that he delivered the money to Adamson. But he said the cash was given to him on June 10 by a man he "never saw before" outside his home.

Howard Woodall, a convicted land swindler, testified that Robinson confessed the Bolles murder to him while both were in the Maricopa County jail.

Defense attorneys attacked the credibility of Adamson and Woodall, emphasizing their criminal records and noting that Adamson would be sentenced to no more than 20 years in an out-of-state prison in exchange for his testimony. Adamson also received immunity from prosecution for several unrelated crimes as part of the agreement.

In a surprise move, Marley was called to testify for the defense. The sunburned, heavy-set liquor distributor denied being angered by Bolles' articles. "He has just another reporter," Marley said. He also testified that he ever expressed a wish to harm Babbitt or Lizanetz and never heard Dunlap make such statements.

However, prosecutors subsequently called a priest who testified that he heard Marley tell then-Gov. Raul Castro in 1975 that he would "do something about" Babbitt. The attorney general had mounted an antitrust investigation of the Arizona liquor industry.

Dunlap's lawyer, Paul Smith, said that as Bolles lay mortally wounded in the wreckage of his dynamited car, "He said it was the Mafia. He said it was Adamson. He said, 'The finally got me.' He didn't say Max Dunlap. He didn't say Kemper Marley."

Bolles' death inspired the creation of a group of reporters from around the country who spent several months continuing his investigations into alleged corruption. The group published a series of news articles about their findings.