For hard-core conspiracy theorists, it was like dying and going to heaven.

One after another, wheeled carts loaded with boxes of once-classified CIA and FBI documents from the investigation into the assassination of President John F. Kennedy were rolled into the second-floor research room of the National Archives yesterday.

A half dozen television cameramen trained their lenses on Archives employees as they passed out white cotton gloves for the researchers and assassination buffs to wear while poring over newly declassified photographs scattered among the more than 800,000 pages of documents concerning the murder in Dallas almost 30 years ago.

Outside, in the corridor, more television cameras were poised to capture the conspiracy theories as they emerged from bulging boxes during the largest disclosure of assassination material yet. A 1992 act of Congress mandated release of the material.

At first blush, it looked like a grab bag of the wildest dreams come true. Pick a box -- any box -- and then close your eyes and reach in for a theory that would make movie director Oliver Stone's heart palpitate.

CIA file DBA-92123, for example: "Allegation that Lee Harvey Oswald met Cuban Premier Fidel Castro in Mexico prior to Assassination of {the} President and that Oswald and Jack Ruby were connected."

With the impressive introduction that the allegation was contained in a letter written by then Defense Secretary Robert S. McNamara to the Warren Commission investigating the assassination, the file recounts a flurry of CIA interest in one Albert D.J. Santalo, an army private. He was said to have told friends at Fort Carson, Colo., that he had information that Oswald met with Castro in Mexico just before Kennedy's death.

After an exhaustive investigation, however, the CIA tracked down Santalo in Baltimore and learned from him that his only source of information on the assassination was an anti-Castro magazine published in New York.

While the magazine had reported that Oswald visited the Cuban consulate in Mexico City before the assassination, neither it nor Santalo had ever claimed that Oswald had met Castro, the CIA report concluded.

The CIA file also appeared to substantiate Santalo's claim that, because he was born in Cuba, his friends at Fort Carson constantly pestered him for "inside" information after the assassination and "were always attaching to his information and opinions a greater value than they merited."

Then there was the inch-thick file on an investigation into "the person who sat beside Lee Harvey Oswald" on his bus trip from Laredo, Tex., to Mexico City on Sept. 26, 1963. It looked promising until the CIA concluded, after minutely examining the life of John Howard Bowen, the seatmate, that he apparently had never even seen Oswald on the bus.

Similarly, a Dec. 13, 1963, CIA report covering the period of Oswald's visit to Mexico City just before the Nov. 22, 1963, assassination, describes a "particularly sinister aspect of Oswald's dealings" with Soviet consular officials while he sought a visa to the Soviet Union.

One Soviet official whom Oswald purportedly contacted, Valeriy Kostikov, was not only a KGB officer but also was believed to have worked for the KGB's Department 13, which the CIA report described as "the department charged with sabotage and assassination."

But later in its report, the CIA said it was convinced that Oswald's contact with Kostikov was "nothing more than a grim coincidence due, in part, to the Soviet habit of placing intelligence men in embassies in positions where they receive a large portion of the visitors and phone calls."

In fact, all five consular officials at the Soviet consulate in Mexico City were known or suspected KGB agents, the CIA concluded.

Despite the numerous dead ends contained in the boxes of documents, assassination buffs said they did not go away from the first day's reading of the files empty-handed.

In a newly declassified 500-page report, for example, the 1979 House Select Committee on Assassinations disclosed that Oswald had a sexual relationship in Mexico City with a Mexican woman working for the Cuban consulate, a woman whom the CIA apparently had targeted for possible recruitment as an undercover agent.

The report cited a CIA source, described only as "reliable," as saying she admitted having intimate relations with Oswald but insisted that she knew nothing about his plans.

The sexual liaison reportedly occurred during Oswald's mysterious visit to Mexico City a month before the assassination, a period that continues to be the subject of speculation and unflagging interest among conspiracy theorists.

CIA documents contained in other boxes, however, said Mexican authorities repeatedly had interrogated the woman and that she had denied any sexual involvement with Oswald. According to the CIA documents, Oswald sought the woman's help in contacting the Soviet consulate to inquire about getting a visa to return to the Soviet Union, where he lived from 1959 to 1962.

G. Robert Blakey, chief counsel to the House committee, said the new material, which criticized the CIA's Mexico City office for "confusing and sometimes contradictory" reporting of its investigation into Oswald's movements, demonstrates that there are "unanswered and unanswerable questions" about Oswald's trip to the Mexican capital.

"Nothing is going to settle this controversy," Blakey told reporters outside the Archives research room. Although the Warren Commission concluded that Oswald acted alone when he shot Kennedy, the House panel's 1979 report raised doubts about the one-gunman theory and said there was evidence that organized crime was involved.

Following today's disclosure of the House Select Committee's report, James Lesar, president of the nonprofit Assassination Archives and Research Center, said, "It certainly complicates the picture and raises a new level of uncertainty as to what was really going on in the crucial episodes in Mexico City."

However, Lesar and other AARC researchers accused the CIA of withholding more than 160,000 pages of assassination documents in spite of the JFK Assassination Records Collection Act of 1992, which called for the disclosure of virtually all of the government's files relevant to the investigation except records that would identify an intelligence agent or confidential sources and subject them to risk of harm.

Jonathan R. Meyers, the center's research coordinator, said one withheld series of documents marked "top secret" apparently deals with the CIA's connections with organized crime in covert operations against Castro.

Some researchers believe Oswald was an agent of a Cuban plot to kill Kennedy in retaliation for attempts by the CIA to use members of the Mafia to kill Castro.

Missing and marked only by pink "document withdrawal" notices were all of the files dealing with purported CIA assassination activities against foreign leaders, files that assassination researchers had expected to be included in the newly released records of the 1975 Rockefeller Commission report on improper CIA activities.

Meyers said the material was supposed to be released under the law but "it's still being withheld from the public."

He also accused President Clinton of "violating the law" by failing to appoint members to a review board that was designed under the 1992 Records Collection Act to compel agencies to release material withheld for unsubstantiated security reasons.

Staff researcher Ann O'Hanlon contributed to this report.