A federal jury weighed the guilt or innocence of Oliver L. North for part of a second day Saturday, then took the rest of the weekend off as the former presidential aide awaited his fate on 12 felony counts stemming from his role in the Iran-Contra affair.

The nine women and three men, guided in their deliberations by a 95-page set of instructions from District Judge Gerhard A. Gesell, arrived bright and early Saturday to resume work in an 18-by-12 room on the sealed second floor of the U.S. Court-house.But there were no clues as to their progress by the time they quit at 12:10 p.m. to return to their downtown hotel to relax, under constant supervision of U.S. marshals, until resuming work Monday.

The jurors, who were asked by the judge to begin by 9:30 each morning, were driven in a van to the courthouse at 8:20 a.m. and started their work at 8:45.

The jury had deliberated for six hours on Friday.

So far, only requests for copies of Gesell's instructions - one for each juror - and for pencils, paper and paper clips have emanated from the jury room, along with the question Friday, "Is lunch at 12?"

They got the materials and the early lunch.

Writing supplies remained a concern Saturday. An unsigned note which covered the jury's return of some documents to the court for safekeeping had this "P.S.: Please sharpen pencils. And we need more pencils and highlighters."

The jurors will be allowed family visits, under marshals' supervision, at their hotel on Sunday. The jurors are forbidden to talk about the case, even among themselves, when they are not in the jury room.

North's trial, nearly three months long, is the first stemming from the late 1985-early 1986 sale of arms to Iran - at a 270 percent markup in price - and the siphoning off of some of the proceeds to the Nicaraguan rebels.

Three other men, former National Security Adviser John Poindexter, businessman Albert Hakim and former Air Force Maj. Gen. Richard Se-cord are awaiting separate trials. Another former national security adviser, Robert C. McFarlane, has pleaded guilty and received two years' probation and a $20,000 fine for withholding information from Congress about the episode.

North, a former Marine lieutenant colonel who served as deputy to both McFarlane and Poindexter, is charged with 12 felony counts, including withholding information from Congress, lying to Attorney General Edwin Meese III about his activities, destroying and altering documents, misusing money entrusted to him and accepting an illegal gratuity - a $13,800 security system at his home.

North, a decorated Vietnam War veteran, testified he was a mere "pawn in a chess game played by giants" and was following orders throughout, even as he was the action officer in both major elements of the Iran-Contra scheme. "I was not stepping in," he said. "I was brought in . . . basically it was a hand-off - `you've got the ball, now run with it.' "

But independent prosecutor John W. Keker told the jury "You have heard a lot about courage at this trial. There's another kind of courage: courage, to admit when you are wrong; courage to admit personal responsibility, courage to admit guilt where appropriate. He has not admitted any of those things; it's time for you do to it for him."

In his instructions, Gesell set specific guidelines for the jury's consideration of each specific count.

For example, on the count that North obstructed Congress by making false or misleading statements to two House committees, Gesell said, "A false or misleading answer to a question may be taken by you as an obstruction if it was made corruptly, with the specific intent to impede the investigation . . . it must be established beyond a reasonable doubt that the defendant acted for the specific purposes of obstructing or impeding."

Similarly, on four counts that North made false statements to Congress or Meese, Gesell said the jury could convict only if it is convinced that "when the defendant made or caused to be made the false statement or representation, he was acting willfully, that is, deliberately or on purpose and not because of mistake, inadvertence or accident."

As for the document destruction charge, the judge said the jury could convict only if it believes North altered or destroyed the materials "with knowledge of the illegality of his conduct."