A federal court juror caused a mistrial in a week-long drug case here yesterday when he acknowledged that he had disregarded the judge's specific instruction to the jury that they avoid reading any newspaper article about the case on trial.

The mistrial in the case against John D. Irby cost thousands of dollars in court personnel salaries and attorneys' fees, according to court officials. The juror told the court he had no explanation for his action.

The jury had begun its deliberations around 11 a.m. Tuesday, the day that a story about the trial appeared in The Washington Star. The story contained information that was on the public record, but some of that information had been excluded from the jurors' hearing -- such as the fact that Irby had a previous murder conviction.

When attorneys in the case saw the story in the afternoon paper, they asked the judge to take action to protect the jury from seeing the story during its deliberations. Irby's attorney, Fred W. Bennett, went so far as to ask that the jury be sequestered during deliberations.

Instead, U.S. District Judge Joseph C. Waddy did as several judges have done in past similar situations here -- prepared a special instrution to be read to the jury explicitly warning its members that they should not read or see any publicity on the case and to stop reading the paper if they come across such an article.

Yesterday morning at the request of attorneys, Waddy asked the jurors if they had been exposed to any publicity about the case. Four replied that they had and the judge asked them individually about the extent of their exposure.

Two said merely that they had heard there was an article about the case, and a third said he had begun reading the article and stopped reading as soon as he realized it was about the Irby case. Those persons probably would have been allowed to continue sitting in deliberation.

However, the fourth juror -- identified in court records as foreman George M. Johnson, of 4335 Douglas St. N.E., a 47-year-old clerk at the National Security Agency -- told the judge he had read the entire article and specifically remembered the sections of it that had not been included in trial testimony.He said only that he was sorry for what he had done, and had no further explanation in court.

Waddy granted a defense request for a mistrial after Irby and Bennett said they did not want the jury to continue deliberating with only 11 members. The jury had earlier reported itself deadlocked, and reportedly was split about evenly for conviction or acquittal.

The mistrial is the second in the Irby case, in which he is accused of selling drugs while on furlough from the Lorton prison complex. The earlier mistrial was granted by Waddy 13 months ago after what he ruled were improper contacts between the prosecutor and defense witnesses during trial.