A U.S. court rule change that takes effect Aug. 1 would allow all federal judges to keep secret a wide range of documents now required to be filled as part of the public record in civil lawsuits.

The rule was adopted as a cost-cutting measure by the powerful U.S. Judicial Conference headed by U.S. Chief Justice Warren E. Burger.

Public interest groups, including news organizations and civil libertarians, are making a last-ditch effect to block or change the rule, which automatically takes effect unless Congress passes special legislation to reject it within the next month.

The material that could be kept from public view includes such documents as pretrial testimony by witnesses, answers to written questions posed by opposing lawyers in a lawsuit and other pretrial materials gathered by attorneys in the stage of civil lawsuits known as the "discovery" process.

The material is filed on a regular basis in the courthouse as a lawsuit develops. It is described and docketed on public files by courthouse clerks and available to any member of the public who asks to see it. Only in rare cases have attorneys convinced judges that the material gathered is so sensitive that it must be treated secretly.

A press group said the material has been the source in the past for hundreds of major news stories, magazine articles, books, television documentaries and various research projects. Many of the most important detailed Watergate revelations, for example, first were made public in the process of a civil lawsuit growing out of the original Watergate break-in.

The public interest groups, including the American Civil Liberties Union and Ralph Nader's litigation group, said the material should continue to be filed publicly because it is taken under the public law powers of the court and is an important public resource.

The judicial conference said in transmitting the rule change to Congress that it was necessary "mainly because of the cost and inconvenience of providing storage for documents that were rarely used." It said at least four U.S. judicial districts already have put some version of the rule into effect, and persons familiar with one of those districts said it has led to substantial budget cuts.

"It often happens that no use is made of the materials after they are filed," an advisory committee on rules changes told the judicial conference. The panel said further that "the copies required for filing are an added expense and the large volume of discovery filings present serious problems of storage in some districts. . . ."

In a letter to U.S. Rep. Robert Drinan (D-Mass.), chairman of a House Judiciary subcommittee, the Reporters Committee for Freedom of the Press said the "excuse offered by the Judicial Conference of the United States is a weak one." The committee, which litigates and monitors various press freedom issues, noted that the materials have been stored "for years" by the court.

The press group, headed by Jack C. Landau, suggested numerous changes that could be made in court procedure short of "the extreme remedy of broad secrecy and destruction of public records" it says it allowed by the new rule. It recommended, for example, that the court could keep the material for five years and then return it to attorneys to keep for another 10 years.

The group also suggested that a summary of pretrial materials available at least be placed on the public record, even if the materials themselves are not made public.

Officials of Nader's Public Citizen Litigation Group and the American Civil Liberties Union said in a separate letter to Drinan that they do not believe the new rule is "entirely clear," but that they are concerned that judges could use it to keep records from public view "in all cases as a matter of course.

". . . In our view, the proper reading of it is that only in those specific instances where the court has made a finding that there is either undue cost or that no good purpose would be served by filing particular papers, may the filing requirement be lifted," said the letter signed by Public Citizen director Alan B. Morrison and ACLU director John Shattuck.

"It is only in that way that the purpose of insuring that court files remain open to the public can be guaranteed," Morrison and Shattuck said.

The two public interest lawyers asked Drinan's subcommittee to issue a report explaining what it sees the rule as meaning and to make it clear that it does not believe filing requirements can lifted "on a wholesale basis." t

They also urged that a monitoring system be set up by Congress to determine to what extent the proposed rule is used "to deny the members of the public inportant information to which they are entitled."

For several decades, the applicable rule has stated tht the materials at issue "shall be filed with the court . . ." The judicial conference proposed more than a year ago that such materials should not be filed at all unless they are actually used in a trial or some other proceeding, but that proposal was withdrawn after various public interest groups complained.

In turn, numerous judges again reiterated their complaint that the material was too cosltly and too inconvenient to store, and asked that the change be reinstated.

The judicial conference then adopted the rule to take effect Aug. 1. It says the material shall be filed with the court, unless a judge -- either on his own or at the request of one of the parties in the lawsuit -- says the filing requirement can ignored.

The opponents to the change warned that the new wording of the rules still endorses wholesale "blanket orders" by judges keeping heretofore public records secret.

Both houses of Congress would have to pass a statute and the president would have to sign it before the rule could be blocked at this point. Legal observers noted tht rarely -- if ever -- has Congress rejected a procedural rule change requested by the Judicial Conference.