A Spanish-surnamed Metro construction worker, who unsuccessfully challenged the ethnic makeup of the grand jury that indicted him, was found guilty in D.C. Superior Court yesterday of first degree murder and carring a revolver without a license.

Gilleamo Hernandez Obregon, 48, was on trial for the shooting death of fellow construction worker Bobby Williams, 41, at a Metro construction site in Southeast Washington last May 10.

In proceedings before Chief Judge H. Carl Moultrie I, Obregon's attorney, Russell Canan, argued that his client shot Williams "as a result of provocations, in the heat of passion and in self defense."

Obregon, who spoke largely through an interpreter, testified that he was frequently harassed by Williams and Williams' cousin, Charlie Williams. He said he feared for is safety and began bringing a.25 caliber pistol to the construction site.

According to testimony in the trial, Bobby Williams, Charlie Williams and Obregon got into a fight on the day of the shooting. Obregon, who said that Bobby Williams had a knife, went to his car and returned with a revolver and shot Bobby Williams seven times, witnesses testified.

Assistant U.S. Attorney Martin J. Linsky, said that the shooting of Williams by Obregon was premeditated. One witness testifying for the government said that Obregon asked a superior shortly before the shooting if he (Obregon) would get into trouble if he shot two men.

Before Obregon's trial began last Wednesday, Canan asked Moultrie to dismiss the murder indictment against the defendant on the ground that the city's grand jury selection process virtually excludes Spanish-surnamed jurors.

Moultrie denied the motion and a jury was empaneled. Persons with Spanish surnames were not on that jury, according to court records.

Sentencing is scheduled for March 13.