Attorneys for nine members of the Black Hebrews religious sect charged with operating a multimillion-dollar crime ring asked for a mistrial yesterday after a prosecutor sent two law enforcement officers who had been witnesses in the case to track down a missing juror.

The latest twist in the 4 1/2-month trial, the longest criminal case ever held in U.S. District Court here, came after government prosecutor J. Michael Hannon sent an FBI agent and a D.C. police officer to help search for a juror who did not report at 9:30 a.m. to join 10 other jurors in their sixth week of deliberations.

The two found the juror, Charles Goodwin, and brought him to the U.S. District Courthouse here, prompting defense lawyers to charge that the security of the jury process had been irreparably breached. The juror said that he had thought that he had been excused from yesterday's deliberations.

"What would the government say if we had sent two Black Hebrews to get" the juror, asked defense attorney Joseph J. Bernard.

The nine Black Hebrews, including the U.S. leader of the group, are charged in a 68-count indictment with conspiring to operate and operating a massive crime ring that trafficked in stolen airline tickets and specialized in counterfeiting credit cards that, along with worthless checks, were used to buy hundreds of thousands of dollars worth of merchandise.

Prosecutors contend that the crime ring was operated to support the group, estimated to have 3,000 to 20,000 members worldwide.

The trial, which is estimated to have cost more than $1 million, has included more than 160 witnesses during nearly three months of testimony. Jury deliberations on Friday passed the record of 131 hours, which was held by the jury in the case of Mary Treadwell, former head of the Youth Pride job training program who was convicted in 1983 of conspiring to defraud the federal government and apartment tenants.

Yesterday's events marked the second crisis in the trial in a week. Chief U.S. District Judge Aubrey J. Robinson, who is presiding over the trial, dismissed juror Bernard Spriggs on Thursday after Spriggs notified the judge that he was no longer able to carry out his duties as a juror because he "disagreed" with the conspiracy law and therefore was unable to apply it to the defendants.

Under a recent federal law, criminal juries may proceed with 11 members if a juror is dismissed with "just cause." But, attorneys said, the case can continue with 10 jurors -- or fewer -- only if all parties agree, and defense attorneys said they would not agree.

Robinson, who sent the rest of the jury home shortly after 2 p.m. yesterday, reconvened attorneys and defendants a short time later when Goodwin arrived at the courthouse.

The session took place at the bench, but sources said Goodwin told the judge that he had spent much of the morning at a medical clinic concerning high blood pressure, keeping an appointment made by a courthouse nurse.

Goodwin told Robinson that he believed that he was excused from deliberations yesterday because the appointment was made by the nurse. He left the clinic sometime after 11 a.m. and was found by the FBI agent and the police officer at a neighborhood pool hall, sources said.

Robinson also interviewed Keith DeVincentis, the FBI agent who was sent to look for Goodwin after U.S. marshals failed to find him. Sources said DeVincentis, who was sent to look for Goodwin by Hannon, the government's main prosecutor in the case, told Robinson that he did not discuss any aspect of the case with Goodwin and that their conversation was limited mostly to the weather.

It was unclear why Hannon dispatched the two men who for more than a year have served as investigators in the case. However, court officials earlier said that they were concerned about Goodwin's physical well-being because of his medical history.

Any contact by a witness or a defendant with a juror must be closely examined to make certain that the jury can reach an unbiased verdict.

Robinson, who has ordered jurors to continue their deliberations at 9:30 a.m. today, is expected to hear defense motions for a mistrial. Three attorneys involved in the case -- six of the defendants, including national leader Warren Brown, fired their lawyers during the trial -- protested the government's action yesterday, but Robinson did not indicate that the government's actions had tainted the jury's deliberations.

Because of the large number of defendants and the charges against them -- the form that the jury is using to reach its verdict has 62 pages -- Robinson has battled since March 10, the day of opening arguments, to keep the trial under control. It took a week to seat the jury. The longest case previously tried in U.S. District Court here, according to court officials, was apparently the Watergate cover-up trial, which ran from Oct. 14 to Dec. 30, 1974.

The judge said at the beginning of the trial that individuals, and not the Black Hebrews group, were on trial and that he would not hear defenses or defense questions based on alleged religious persecution. Enforcing that dictum has required hundreds of bench conferences with attorneys. So that the jury would not have to leave the courtroom for each bench conference, defendants and some attorneys listened to the proceedings through earphones.

Keeping order during the trial became more complicated when five of the defendants fired their attorneys during the third month of the trial. Brown dismissed his attorneys the day after Memorial Day, soon after the defense presentation began.

Robinson ordered the dismissed lawyers to continue as "advisory counsel" through the case, and the bill for the defendants' court-appointed lawyers is believed to be nearing the half-million-dollar mark.

When the trial opened, Robinson remarked repeatedly that he hoped that it would end by July 4.

He apparently believed that it would end sooner, and he set another trial involving six Black Hebrew women to begin in late June. That trial, in which the women are charged with conspiracy, wire fraud and aiding and abetting what prosecutors allege was a scheme to defraud local welfare agencies of child assistance checks, began on July 8 and has been adjourned repeatedly because of the first jury's deliberations.

"The first trial is beginning to affect the second trial," an attorney defending one of the women said. "I don't know how much longer this can continue without affecting the jury" in the women's case, he said.

A third trial, in which nearly 20 Black Hebrews are charged with fraud in connection with an alleged scheme to defraud MCI and other long-distance telephone companies, is scheduled to begin in mid-August.