Under the JFK Records Act, the FBI is about to release the first of what will eventually be more than 1 million pages of documents related to President John F. Kennedy's assassination in 1963.

All government records concerning the assassination should carry a "presumption of immediate disclosure," according to the law, enacted in October 1992. As a result, files previously censored in whole or in part by the FBI will now be made public in their entirety, whether directly relevant to the assassination or not.

About 95 percent of the "core files," totaling about a half-million pages, have been available to the public for more than a decade, FBI officials say. The other half-million-plus pages include records submitted to the House Assassinations Committee and other investigating panels in the 1970s, such as documents concerning organized crime figures.

The records were scheduled to be turned over to the National Archives last August, but FBI officials say they did not realize the task they faced in screening the records under the standards of the new law and in meticulously labeling each document. They say they have had 60 people working on the project since April and now have 87 assigned to it, working two shifts a day, seven days a week.

"We want this information out," said FBI Assistant Director William E. Baugh Jr. "We have the largest and most interesting bloc of information on this subject." Baugh, who is in charge of the FBI's information resources division, said the JFK task force is consuming about 20 percent of all the overtime that the entire bureau has at its disposal.

"Every division, every field office is involved," Baugh said.

However, it will be months before the FBI finishes its first cut on the collection, sending most of it to the Archives while withholding release of the documents it considers the most sensitive.

"We will have more than 500,000 pages released in the next few months and we are working toward completion by July 4," said Terry T. O'Connor, one of the JFK task force directors.

O'Connor and co-director John A. Hartingh said the records of the House Assassinations Committee and those of other investigative panels of the 1970s will be reviewed last. They indicated that the organized crime files will be withheld until the bureau gets a ruling from a special review board set up under the law on whether they must be made public.

The five-member review board, nominated by President Clinton, is still awaiting Senate confirmation.

The files to be released within the next few days concern Jack Ruby, the Dallas nightclub operator who killed Lee Harvey Oswald on Nov. 24, 1963, two days after Oswald was arrested and charged with killing the president.

Baugh said the FBI's 21,224- page "headquarters file" on Ruby will be the first records to be made public at the Archives. Of that, only 31 pages will be withheld in their entirety, some because they are tax records, others because the information came from foreign governments. Another 364 pages, Baugh said, have been partly censored and disclosure of the blacked-out segments will be "postponed" until the review board has a chance to rule on them.

The FBI's field office files on Ruby, about 52,000 pages, are likely to be turned over to the Archives later this month.

Beyond the Ruby files, the bureau's "core files" also include documents from FBI headquarters and field offices, many duplicated from file to file: on the assassination investigation (280,000 pages); Oswald (270,000 pages); the Warren Commission (45,000 to 50,000 pages); and "related materials" (25,000 pages), such as records on Oswald's wife, Marina, and his mother, Marguerite.

Some previously censored files will also be made public. For example, a Dec. 3, 1963, internal FBI memo on Ruby was half-censored when first released in 1980. It concerned a Hollywood publicity agent who was promoting a biography of Ruby to be written by an author who had previously written a book on a California killer.

The full memo, now to be released, shows that the blacked-out portions primarily concern the alleged Communist Party backgrounds of the publicity agent, his two brothers and a sister-in-law. Another deletion identifies sources who described the prospective writer as an alleged publicity hound.

O'Connor said the FBI is still withholding the names of FBI informants and others who were expressly promised confidentiality by authorities. The law says an informant's name is to be withheld only if the person is alive and disclosure "would pose a substantial risk of harm to that person," but FBI officials say they will leave such determinations to the review board.

The bureau is also withholding information that it feels would constitute "an unwarranted invasion of privacy," leaving the review board to decide, as the law states, whether "the public interest" still requires disclosure.

As an aid to researchers, Baugh said, the 87-member JFK task force is compiling an inventory sheet indexing the documents in each thick volume or section that will enable researchers to take a document from a headquarters file and track it down in a field office file even though the numbering systems differ.

The law was passed largely as a result of congressional indignation over Oliver Stone's 1991 movie "JFK" and its allegations of wide-ranging government involvement in the Kennedy assassination.

FBI Director Louis J. Freeh wants "the fullest disclosure possible," Baugh said. "We've spent about $1.5 million on this so far. Ours is going to be the most comprehensive and thorough collection {at the National Archives}."