An Arlington jury began deliberating yesterday in the murder trial of Joseph N. Martin, accused of hiring another man to kill a young couple in 1977. The trial, which has lasted more than six weeks, culminates one of the lengthiest and costliest prosecutions ever in Northern Virginia.

Martin, a 28-year-old former insurance salesman, could be sentenced to death if convicted.

The jury deliberated for five hours before retiring to a motel for the night. It will resume its consideration this morning.

The key witness at Martin's trial was Richard Lee Earman, a former Northern Virginia real estate salesman who was acquitted by a jury in 1977 of murder charges in the case.

Earlier this year, Earman, 36, pleaded guilty to a murder conspiracy charge as the result of bargaining with the Arlington prosecutor. He testified he shot the couple -- Alan Foreman and Foreman's fiance, Donna Shoemaker -- in a murder-for-hire scheme initiated by Martin.

The bullet-riddled bodies of Foreman, 26, who worked for the same real estate company as Earman, and Shoemaker, 25, were found in the garage of their Nirth Arlington home in May 1977.

Earman is scheduled to be sentenced for murder conspiracy Dec. 21 and could receive up to 10 years in prison. He was barred from being retried on a murder charge by the constitutional protection against double jeopardy.

Prosecutors argued that Foreman's death climaxed a complex insurance scheme designed by Martin to defraud the New Ork Life Insurance Co. and provide the means to finance "a flashy life style way beyond his income." Part of the scheme allegedly involved a $56,000 life insurance policy Martin sold Foreman. Earman was to receive $15,000 as the triggerman, the prosecution asserted.

Martin, now a Las Vegas, Nev., resident who is free under $50,000 bond, did not testify.

His attorneys, Louis Koutoulakos and Gerard F. Treanor Jr., portrayed Martin as an occasional business partner of Foreman's Martin's admittedly fraudulent insurance scheme, Koutoulakos said yesterday in his closing arguments, was in no way "intertwined" with the slayings.

Earman, one of more than 100 witnesses who testified at the trial, told the jury he and Martin plotted Foreman's death over lunch at various Tysons's Corner restaurants. He testified that when he told Martin he might have to kill Shoemaker as well because the couple frequently was together, Martin replied, "beautiful, beautiful," because that would deflect suspicion from the insurance motive.

Earman calmly told of shooting the couple in te head at point-blank range after the three returned from Tramp's, a Georgetown disco.

Prosecution in the case began in 1977, with both Martin and Earman the murder defendants. The charges against Martin were dropped by prosecutor William S. Burroughs Jr. in the middle of Earman's trial.

Burroughs, who has been replaced by a special prosecutor for Martin's current trial because he was a prosecution witness, told the jury he dropped charges against Martin two years ago because Martin told him he got a threatening note from an unnamed person several days after the murders. Burroughs said this note, which he said he never saw and Martin claimed had been destroyed, persuaded him at the time of Martin's innocence.

The jury at the 1977 trial went on to acquit Earman of murder.

Under cross-examination at Martin's current trial, Earman, who is collaborating on a book about the slayings, admitted that he repeatedly lied to police and prosecutors to make his story sound more convincing and to confuse the authorities.

Circuit Court Judge Charles S. Russell cautioned the jurors to consider Earman's "uncorroborated testimony . . . with great care."

Defense attorney Koutoulakos referred to Earman as "this liar they're using to convict Mr. Martin." In his closing arguments he said, "there was a conspiracy all right. Mr. Earman decided he was going to hit the big one with this book he's writing. Yes, Joe messed around with those insurance policies, but there's absolutely no evidence to tie him in with those murders."