An Arlington judge yesterday ordered county prosecutors to turn over evidence that attorneys say is crucial to the defense of Joseph N. Martin, 28, a former Northern Virginia life insurance salesman scheduled to stand trial July 9 on charges that he murdered an Arlington couple in 1977.

Among the documents that Judge Charles S. Russell ordered prosecutors to file by June 8 are "written, recorded or oral statements or confessions" made by Martin.

A Las Vegas resident, Martin has pleaded innocent to charges that he hired Richard Lee Earman to kill Alan Foreman, 26, and Donna Shoemaker, 25, in order to collect on a $56,000 life insurance policy.

At the request of Martin's attorney Gerald F. Treanor, Russell ordered Prosecutors to discloes "the precise terms of any promises or suggestions of leniency" made by county prosecutor William S. Borroughs to Martin or Earman.

Earman, a former Northern Virginia real estate salesman, was acquitted of murder after a celebrated trial, but recently pleaded guilty to a charge of conspiring with Martin to kill the couple.

Earman recently testified that he shot Foreman and Shoemaker to death in return for a promise of $15,000 by Martin. Earman, in jail awaiting sentencing next month, faces a maximum 10-year prison term that will be served in a federal prison, under terms of a controversial plea bargain negotiated with Burroughs.

Martin, who attended yesterday's hearing, is free on $50,000 bond.