The first of five suspects charged in the execution-style slayings of three District of Columbia men in Prince George's County in October, 1975, was convicted yesterday of three counts of murder.

A Prince George's Circuit Court jury returned its verdict against Willie Lee Jones, 25, of 5758 Ames St. NE after deliberating almost two hours. The jury also found Jones guilty of four counts of kidnaping and three of using a weapon during the commission of a crime.

The fatal shootings of David Alan Dock, 21, of 5019 B St. SE; Alvin Jones III, 22, of 132 57th P1. SE, and William Anthony Cunningham, 21, of 5739 East Capitol St., occurred Oct. 24, 1975, in a wooded area off the 6600 block of Deputy Lane and George Palmer Highway.

Assistant State's Attorney Robert C. Bonsib, who prosecuted Willie Jones, said the slayings followed the theft of $400 worth of cocaine or heroin from the defendant's sister, Johnie Mae Jones, 21, of 2701 Bruce P. SE.

The prosecution's chief witness, Ronald Swayne, testified at the two-day trial that he was abducted along with the three other victims and was being held captive in the trunk of his car when he heard gunshots. The victims were slain with a sawed-off shotgun and two handguns, the prosecution said.

According to testimony at the trial:

Swayne and the other three men were lured into Prince George's County on the evening of Oct. 23, 1975. When they arrived at the Gregory Estate Apartments in Seat Pleasant they were threatened with guns. Two of the men were forced from the apartment into the trunk of a blue Cadillac while two others, including Swayne, were forced to lie face down on the rear floor of the car with a blanket over them. They were driven to the 6200 block of Deputy Lane and forced from the car.

According to prosecutor Bonsib, the sister of the defendant then identified three of the four men as those who stole the drugs. The sister, defendant Jones and Swayne drove back to the District where Jones' sister was dropped off, Bonsib said. He said the defendant and Swayne then returned to the wooded area where, Swayne testified, he heard the shots.

According to Bonsib, Dock was the only one to die at the scene of the shootings. He said Alvin Jones was able to crawl to a nearby gas station and call for help. Jones died en route to Prince George's General Hospital.

Cunningham was able to make a statement to a Prince George's police officer shortly before he died in the hospital, Bonsib said. The prosecutor referred to that statement as a dying declaration, and said it identified Willie Jones as one of the slayers. In addition, Jones made two statements to police that were admitted as evidence at his trial.

Defense attorney Benjamin Wolman said he will appeal yesterday's verdict and that an issue in the appeal will be the fact that Jones did not have legal counsel present during an interrogation by county police.

Jones' sentencing by Judge Jacob Levin was scheduled for Feb. 4. He could receive up to life prison sentences for the murder convictions; up to 120 years for kidnaping, and another 60 years for using a handgun in the commission of a crime.

Still to be tried on murder, kidnaping and weapons charges are James H. Person, 20, of 5931 Ames St. NE, and Roland Neville Godwin, 22, of 1320 Ingraham St. NW.

Charged as being accessories before the fact of murder are Jones's sister and Towanna Matthews, 22, of Seat Pleasant.