The agency that sets procedure in the federal courts is considering a proposal to require judges to close criminal trials whenever they believe openness might prejudice a jury.

The same proposal would allow judges to order the media not to report certain proceedings and to hold news organizations in contempt of court for violating such an order.

The proposal, still in the discussion stages, has already prompted threats of lawsuits from media organizations which argue that it violates Supreme Court rulings as well as the judiciary's policy-making procedures.

The new rule would let judges close such pre-trial and trial proceedings as bail determinations, questioning of potential jurors and arguments over admission of evidence that have traditionally been conducted with the jury out of the room, but without fetters on press or public.

The argument is that subsequent media reports of such proceedings can still end up influencing juries.

The rule, which would not apply to the state and local courts in which most criminal trials are held, was proposed by a subcommittee of the Judicial Conference of the United States, the policy-making arm of the judiciary made up of federal judges from across the country and headed by Chief Justice Warren E. Burger.

It may be modified after public hearings, which are currently under way, and must be approved by the full conference and the Supreme Court (without the usual adversary proceeding) before taking effect.

Congress may veto rule changes as well.

The proposal says that judges "shall order that the public, including representatives of the news media, be excluded" from proceedings if there is a "reasonable likelihood that dissemination of information" would interfere with a defendant's right to a fair trial by an impartial jury. That "reasonable likelihood" standard is considered one of the most flexible in the law.

Before closing, the proposed rule says judges must weigh other means of preserving jury impartiality, such as moving the trial elsewhere or sequestering the jury.

But in a commentary accompanying the proposal, a Judicial Conference advisory committee on criminal rules noted that these alternatives are not necessarily "preferable to closure."

As a halfway measure, the judges could allow reporters and members of the public to remain in a courtroom on the condition that they not disclose what they saw or heard until the judge said so. Anyone violating such a condition could be held in contempt.

Under the proposal, a judge could close the trial over the objection of the defendant, though this is strongly discouraged.

Members of the press or public would be able to object only if they were present at the time closure was suggested. They would be entitled to a hearing before the judge, but the same judge could seal both the substance of the hearing and his own findings, order the press not to report either and bring contempt proceedings against violators.

The Supreme Court, in the 1980 Richmond Newspapers opinion, ruled that the First Amendment requires open trials except in extraordinary circumstances. It did not identify those circumstances.

The court has also refused to allow court orders restraining the press from publishing.

Opponents cited those cases in denouncing the proposed rule. The Reporters Committee for the Freedom of the Press and the Associated Press Managing Editors have also accused the judicial conference of overstepping its own authority by even considering the rule. The conference's powers, under the law, are supposed to be confined largely to procedural, not constitutional, judgments.

"Should you go forward with this ill-advised rule, we are prepared to challenge it in court," said a statement read by the two organizations at hearings Wednesday.

The conference's advisory committee on criminal law is chaired by Norfolk U.S. District Judge Walter E. Hoffman. Its members are U.S. Judges Roger Robb, Eugene A. Gordon, William L. Hungate, Frederick B. Lacey, Leland C. Nielsen and Russell E. Smith.

Other members are D. Lowell Jensen, assistant U.S. attorney general; James F. Hewitt, federal public defender; Wade H. McCree, Jr., former U.S. solicitor general, Leon Silverman, an attorney, and Fred M. Vinson Jr., an attorney and former Justice Department official.