Richard Lee Earman, a former real estate salesman who was acquitted by a jury of murdering an Arlington couple, was arrested again yesterday by Arlington police and charged with conspiring to murder the couple.

The police investigation of the case was revived with the assistance of H. Kaya Ploss, a Polish-born writer who lives in the District of Columbia and who has been writing a book on Earman's life.

Tips and leads she has provided over the last year fueled the investigation at times when it appeared to be stalled, police said. "If it wasn't for her, the investigation would have been dead," said one source close to the investigation.

Ploss wrote to Virginia Gov. John N. Dalton complaining about the manner in which the investigation was being handled and Arlington police supplied her with a shotgun for her own self defense as her involvement in the case grew.

She has said that threats have been made on her life, and recalled an instance when an unidentified called told her that two people were dead already and one more death would not make any difference.

The new charge, conspiracy to commit a felony, carries a penalty of up to 20 years imprisonment. County Commonwealth's Attorney William S. Burroughs said yesterday there is "ample legal precedent" to try Earman on the conspiracy charge even though he has been found not guilty of the murders.

Earman's arrest accurred at 2 a.m. yesterday at the Arlington County Courthouse, 11 hours after he voluntarily appeared to talk with Burroughs and police about the murders of Alan Foreman and Donna Shoemaker.

The couple was found shot to death in May 1977 in Foreman's car, which was parked in the garage of his North Arlington home. Earman was indicted shortly afterward, but was found not guilty after a two-week trial that ended last October.

The sudden arrest of Earman is the latest in a number of bizarre events that have marked the murder investitation.

Burroughs and the Arlington police had been at odds for months over how to proceed on the case. Their dispute reached the point that police complained to the Virginia state attorney general's office that Burroughs was impeding their progress.

Virginia Attorney General J. Marshall Coleman ordered state police into Arlington to investigate the dispute and months later closed the case after state troopers concluded Burroughs was not guilty of any criminal conduct.

Earman's arrest took him by surprise, according to sources close to his family, and apparently indicated that prosecutor Burroughs and county police have resolved some of their differences over the case.

Earman yesterday was being held on $2,000 bond in the Arlington jail, where he spent nearly four months last year awaiting trial. He appeared briefly in Arlington General District Court yesterday, and his case was continued until next week so he could get a lawyer.

According to family sources, Earman had been despondent about being unable to get steady work.

Earman, 35, a powerfully built, bespectacled man, has been staying primarily with his parents in Falls Church and living off unemployment benefits and odd jobs as a gardemer and tennis instructor, according to sources close to the family.

A month ago Earman was arrested in Stanton, Mich. and charged with breaking and entering, but those charges were subsequently dropped. He had served more than five years in Virginia prison after being convicted for his part in the 1968 Beltway bulgaries in the Washington suburbs.

In an interview with the Washington Post earlier this week, Earman said he had been in Michigan visiting friends, and wanted it known that the charges there which were publicized in Washington, had been dropped. Earman accused Arlington police and Burroughs of influencing Michigan authorities to make the arrest and hold him on $25,000 bail. Burroughs yesterday said he would not comment on Earman's allegations.

While in custody in Michigan Earman submitted to a lie detector examination a tthe request of Arlington Detective David Green, the principal police investigator on the Virginia case.

Earman's desire to talk with authorities on Thursday comes less than a weeek after the arrest in New Jersey of Herbert Wallace Jr., another man police have sought to question in connection with the murders.

Wallace, 38, was arrested inside a Medford, N.J., bank last Saturday and charged with robbery and assault. Green interviewed Wallace earlier this week, through a New Jersey court order, obtained Wallace's fingerprints and samples of his hair.

As of late yesterday no other arrest warrants had been issued in the case and Burroughs would not say when, or even whether, any would be.

Earman, contacted by The Washington Post through an intermediary yesterday, declined comment.

The heart of the dispute between police and Burroughs has centered over the role of yet another figure, Joseph N. Martin.

As originally outlined in court papers, police alleged that Foreman and Shoemaker had been killed by Earman in order to collect Foreman's $56,000 life insurance policy. Martin, a life insurance salesman, had sold Foreman the policy a few months before his death. Martin was indicted along with Earman.

Burroughs dropped charges against Martin during Earman's trial, but police continued to investigate and pressed Burroughs to indict Martin again. When Burroughs refused, citing lack of evidence, the police explained their case to Coleman's aides.

Martin has reportedly sold his home in Loudoun County and moved with his wife to Las Vegas. He has maintained he is innocent of any connection with the murders, and has said that he was prompted to move, in part, because police would not leave him alone. CAPTION: Picture, RICHARD LEE EARMAN, . . . held on $2,000 bond