A 19-year-old Virginia man, asked to explain his comments about the shooting death of a Lorton construction worker, testified yesterday that he knew he did not have to give an officer a statement, but "I told him what happened."

Robert Eddie Grogg, wearing a red plaid shirt, blue jeans and tennis shoes, was almost dwarfed by the witness chair. He answered softly as Commonwealth's Attorney Robert F. Horan Jr. questioned him.

Defense attorneys had put Grogg on the stand in an effort to persuade Fairfax County Circuit Court Judge J. Howe Brown Jr. to suppress the youth's 26-page statement on the grounds that it was not made voluntarily or knowingly.

Brown denied the motion, saying, "He may not have understood some of the words" but "the evidence clearly shows that his rights were fully explained."

Grogg and his 16-year-old brother Thomas each have been charged with first-degree murder, use of a firearm in the commission of a felony and robbery in the death of Hallie Hollis, 28. Attorneys for Thomas Grogg are trying to suppress a similar statement made by their client.

Fairfax County police investigator J.A. Hughes testified yesterday that Robert Grogg told him that he and Thomas argued about which one of them would kill Hollis, who had picked them up in his red Ford Torino on Oct. 20 while they and two juvenile girls were hitchhiking on Rte. I-95. He said "his brother . . . more or less won the argument," Hughes said.

Hughes said Robert Grogg told him that when his brother became nervous after shooting Hollis nine times in the back of the head, Robert Grogg said to him: "I told you I should have shot him . . . . " During his statement, said Hughes, Grogg showed no emotion.

Hollis' Ford Torino was found near a lake in Volusia County, Fla., according to Hughes. Divers searched the lake and found a license plate, some painter's clothes and a pair of black roller skates with the name of Eddie Grogg written inside.

Richard F. MacDowell Jr. and Timothy J. McGary, Grogg's attorneys, also argued yesterday that there was no probable cause for their client to be arrested on the initial grand larceny and robbery charges.

But Fairfax County Officer C.F. Pfeiff, who also testified yesterday, said Grogg and the others were arrested near Sarasota, Fla., after the laundry number in the painter's pants matched a number in clothing issued to Robert Grogg by his employer in Annandale.

Judge Brown, pointing to the painter's clothes, the skates and the fact that the four persons were seen together, said there was indeed probable cause and called the investigation "good police work."

When attorney MacDowell questioned Grogg, who has an eighth grade education and lives in the Fredericksburg, Va., area, if he had been read his rights to have an attorney present and remain silent, he responded: "I don't know what you're talking about." And when asked if he understood those rights as read to him by a judge he said, "half and half."

But when questioned by Horan, Grogg responded "yes, sir" when asked whether he knew anything he said could be used against him. And when asked if he knew he could remain silent, he also said "yes, sir," adding that he was told he might as well talk because all the others had already done so.

Brown set Robert Grogg's trial for March 4. Thomas Grogg is scheduled for trial on Feb. 18.