Two men, one of them serving a prison sentence, have been indicted by an Alexandria Circuit Court grand jury on charges of killing a businessman three years ago in a murder-for-hire scheme.

If convicted, the men could be sentenced to death in the slaying of William Bensen Young, 54, a vice president of the Suburban Electric Corp. of Alexandria. Young, who lived in Bethesda, was shot in the chest Nov. 27, 1981, during a robbery at the firm's office at 4114 Wheeler Ave.

Accused in the indictments, handed up Monday, are Thomas Ebron, 25, who is serving a three-year sentence for armed robbery in the District of Columbia's Lorton prison complex, and Charles Joseph, 35, of the 4200 block of 14th Street NW.

Prosecutors and police would not disclose any details of their investigation, nor would they say who they believe paid to have the killing carried out.

In addition to murder and conspiracy to murder, Ebron and Joseph were charged in the indictments with three counts of robbery and three counts of use of a firearm. Ebron is accused of doing the actual shooting.

A third man, Ralph Threatt, 45, of l42 W St. NW was arrested in April on a charge of conspiring to murder Young. He was released under $15,000 bond, and Commonwealth's Attorney John Kloch said yesterday Threatt's case is still before a grand jury. Kloch would make no further comment on the charge against Threatt.

According to court records, while Threatt was in the D.C. Jail waiting for his bond to be posted he wrote a letter to Alexandria Circuit Court Judge Donald Kent saying: "The prosecuting attorney knows for a fact that I did not commit this crime nor did I gain money from it. All of the evidence is hearsay."

His attorney, Harry Hart, declined yesterday to comment on Threatt's whereabouts.

At the time of the slaying, police said, two men who were with Young in the company office were robbed. In an affidavit filed in 1981, one of the men, Frederick H. Ramsay, said: "Two men entered the building and pointed a gun at us. They demanded our money and said to get in the corner. I turned around and heard a shot and then looked back . . . . "