Huddling in a park near Union Station four years ago, Thomas Ebron and Ralph Threatt discussed killing Alexandria businessman William B. Young, the two men testified yesterday.

Young's partner, Frederick H. Ramsay -- who had taken out a $150,000 life insurance policy on Young's life with a double indemnity clause for accidental death -- wanted Young dead and they were going to help him, the two told an Alexandria Circuit Court jury.

Ebron and Threatt, both of the District, were charged in the Nov. 27, 1981, death of Young, 54. Now, after extensive plea bargaining with the government, they are serving as key witnesses in Ramsay's murder trial. Ramsay has pleaded not guilty.

Ebron, 26, pleaded guilty last week to first-degree murder after testifying that with a single shot from a .22-caliber semiautomatic rifle, he killed Young. Prosecutors say that in exchange for his testimony in this week's trial, they will not seek the death penalty.

Threatt, who told the jury he purchased the rifle and hired Ebron and another District man, Charles Joseph, 36, to kill Young for Ramsay, has been granted immunity in the case. "He Ramsay said he was having some problems and wanted to get rid of Bill," Threatt testified. " . . . He wanted him liquidated. He just wanted him dead."

Threatt, 44, worked as an electrician for Suburban Electric Co., the firm in which Ramsay served as president and Young as vice president. The company, now defunct, was having financial difficulties at the time of Young's death, according to court records.

"About a week before this thing murder occurred, we met," Ebron tesified yesterday. "I was in the back seat. Threatt was driving and Ramsay was in the passenger seat."

Ebron, who was ushered into the courtroom in leg irons, told detectives in sworn affidavits that Threatt offered him $10,000 to kill Young, but that he was paid only $1,500.

Ebron will take the stand again today because before the prosecutor and defense attorneys questioned him, Judge Donald M. Haddock dismissed the 14-member jury. The defense contended that because an Alexandria policeman had shown Ebron a photograph of Ramsay before Ebron was asked to identify him in a lineup, he should not be permitted to identify Ramsay in court.

After hearing Ebron's testimony, Haddock ruled that Ebron should be allowed to identify Ramsay.

Defense attorney A. Albert Ahern argued in his opening statement that the government's entire case is based on the testimony of criminals and therefore not credible. Ahern said he was not disputing the actions of Threatt, Ebron and Joseph, who also pleaded guilty to first-degree murder. "I am arguing," Ahern said, "that Ramsay had nothing to do with it."

Ahern told the jury that the key witnesses in the trial were only pointing the finger at Ramsay to get time off their sentences.

Assistant Commonwealth's Attorney Randolph Sengel said he will recommend that Ebron be sentenced to life and Joseph be given a 46-year prison term. Premeditated murder committed for financial gain is punishable by death in Virginia, but officials have said they will not seek the death penalty if Ramsay is convicted.

Ramsay, 41, of 6609 Hackberry St., Springfield, is expected to take the stand later this week.

Massachusetts Mutual Life Insurance Co. unsuccessfully contested awarding Suburban Electric the $300,000. Officials contended in a civil lawsuit that because Ramsay was being investigated by the Alexandria Police Department as a prime suspect in the murder-for-hire scheme, the company should not have to pay. A circuit court judge ruled last year, however, that because the long murder investigation had produced no conclusive evidence, the company must pay the award.

The planning of the murder began at a neighborhood park near First and R streets NW and spanned a one-month period, Ebron and Threatt testified.

Young's wife, Jacqueline, told police that her husband had telephoned her at their Bethesda home shortly before he was killed and told her someone was following him.

On the day after Thanksgiving in 1981, Young was fatally shot in the chest as he stood in his office at Suburban Electric, 4114 Wheeler Ave.