The federal judge presiding at the trial of nine members of the Black Hebrews religious sect charged with operating a multimillion-dollar crime ring refused yesterday to grant a mistrial in the 4 1/2-month-long case but ordered the jury sequestered for the remainder of its deliberations.

The decision by Chief U.S. District Judge Aubrey J. Robinson Jr. came amid allegations that a personal representative of Rep. Mervyn M. Dymally (D-Calif.) may have contacted a juror improperly in a hallway outside the courtroom.

Defense attorneys asked Robinson to declare a mistrial Monday, contending that the government tampered with the jury after a prosecutor sent two law enforcement officers who were key government witnesses to search for a juror who did not report that morning.

Yesterday, Claudette Johnson, a local business consultant who said she was "assisting" Dymally with the case, testified that Monday afternoon she saw a man she later learned was the missing juror, Charles Goodwin, being escorted into the courthouse by FBI agent Keith DeVincentis and that she overheard them talking.

Saying she was "shocked and appalled" that DeVincentis was with a man she was "95 percent sure" was a juror, she said she approached Goodwin to make certain he was a member of the panel.

Assistant U.S. Attorney J. Michael Hannon, who had sent DeVincentis to look for the juror, said Johnson's alleged contact with Goodwin showed there are "persons acting as vigilantes outside to supervise the deliberations of the jury" and asked that its members be sequestered.

Johnson testified that Dymally, a three-term member of Congress and former California lieutenant governor, is interested in the trial because of his membership on the House Foreign Affairs Committee and his concern for several thousand members of the Black Hebrew religious sect who live in Israel but do not have legal status in that country.

David Johnson, Dymally's press spokesman who is no relation to Claudette Johnson, said last night that Claudette Johnson has served as a "liaison between the congressman and the people who are under trial," keeping him updated. He said she is not on Dymally's paid staff and did not know how the arrangement originated, but believed that Dymally was approached by Claudette Johnson.

David Johnson said she also set up a meeting at the jail among Dymally and the five defendants who are incarcerated on the day of closing arguments in the case. Dymally was en route to Washington from California last night and could not be reached for comment.

The jury began deliberations June 6 after closing arguments the two previous days.

Hannon also presented a letter on House stationery with Dymally's signature that stated Claudette Johnson was "assisting" him in the case. Hannon said Johnson used the letter to facilitate her contacts with jailed Black Hebrews and to arrange a recent meeting at the jail for them with Nation of Islam leader Louis Farrakhan.

Among those on trial is Warren Brown, also known as Prince Asiel, who is the national leader of the Black Hebrews group. Court records in Chicago show that when Brown and several other defendants were arrested there last year on the charges now before the jury that Dymally offered to put up a $100,000 house in Los Angeles as part of a surety bond.

In denying the request for a mistrial, Robinson said after a daylong hearing that he found "no credence at all" in accounts by Johnson and another witness that the FBI agent and the juror had a running conversation.

Robinson said he could not find that irreparable harm was done to the sanctity of the jury's deliberations and noted that if anyone's case had been damaged it was the government's, not the defendants'.

"The government fouled up by sending the FBI agent and the police officer, but the blame is now put on the defense and the jury is suffering for it," said defense attorney Joseph J. Bernard.

The Black Hebrews' trial, the longest ever in U.S. District Court here, involves nine members who are charged with conspiring to operate and operating a continuing criminal enterprise that prosecutors allege trafficked in stolen airline tickets and used fake credit cards and worthless checks to buy hundreds of thousands of dollars worth of goods.

Robinson also is presiding over another Black Hebrew case involving six members charged with conspiracy in an alleged scheme to defraud local governments of welfare money.

Dymally's former wife, Amantha Dymally, testified as a character witness Thursday for one of the defendants in that case.

She said her former husband asked her to allow the defendant, Darlene Wilson, to live at her Los Angeles home while Wilson worked on two projects for him, a dinner for Shaw University and a fund-raising dinner for his reelection effort.