If you want the inside story about John Dillinger and his gang, Helen Ann Near is the person to call.

She also can introduce you to the worlds of Charles (Pretty Boy) Floyd, Alger Hiss and Whittaker Chambers, Soviet spy Kim Philby and billionaire Howard Hughes -- all as seen through the lenses of the Federal Bureau of Investigation.

A soft-spoken, unfailingly patient veteran of nearly 33 years at the bureau, Near is in charge of the Reading Room at FBI headquarters, a treasure trove of nearly one million pages of FBI documents churned up by the Freedom of Information Act in recent years.

The Reading Room itself isn't easy to find. You can't enter from the street. You're supposed to make appointments 48 hours in advance. And if more than six people show up on a given day, they're going to feel cramped. Room No. 1218 at the FBI has more space for its movable bank of 7-foot-high bookshelves than it does for people.

But it usually isn't crowded. The scholars, students, snoops and what-have-you who visit the modest sanctum are vastly outnumbered by those who deal with the bureau by mail. The Reading Room rarely gets more than one or two customers a day.

For those interested in current or near-current history, the topics are fascinating. The seven-page list of topics in the stacks ranges from the American Indian Movement (17,725 pages) to the Weather Underground (420). Recent additions include Ernest Hemingway (a "personal informant" of the U.S. ambassador to Cuba during World War II), Huey Long and the shooting of George C. Wallace.

There is, of course, more upstairs -- much more, available on request. The subjects in the stacks of Room 1218 vary like a bookstore's, although not quite so frequently.

"It's like the Sears catalogue," Near says. "If no one buys a certain item that was listed the previous year, it's going to be taken out."

In all of 1979, for instance, no one bothered to sit down with the file on long-missing aviator Amelia Earhart. The next year, she was purged from the Reading Room, along with the Freedom Riders, the 1967 Detroit riots, the integration of the Little Rock, Ark., schools in the 1950s, and Elvis Presley.

Presley has made a comeback, though, bigger than ever. There were only 87 pages of FBI documents on him when he was yanked in 1980. Now he's back on the charts with an 807-page file.

Presley, according to one memo, offered in 1970 to become an FBI informant, saying that the "filthy unkempt appearances and suggestive music" of the Beatles were responsible for many problems the United States was having with young people. The FBI credited Presley with "sincerity and good intentions," but advised Director J. Edgar Hoover not to meet with him because of Presley's habit of wearing "all sorts of exotic dress."

As Near points out, some of the files grow thicker through additional FOIA requests of broader scope. Sometimes, court litigation will squeeze out long-suppressed details. For some subjects, such as the assassinations of John F. Kennedy (220,436 pages) and the Rev. Martin Luther King Jr. (39,237 pages), processing under the FOIA takes more years than the requestors -- and the requestees -- care to count.

The most popular file in the Reading Room these days is the 155,500-page compendium on Julius and Ethel Rosenberg, the subjects of unending controversy since 1953 when they were executed at Sing Sing following their conviction on charges of delivering atomic secrets to the Soviet Union.

Tied for second place are documents about the Hiss-Chambers espionage case of the same postwar era and the O&C (Official and Confidential) files of the late director Hoover.

There is a 317-page compendium of Hoover's O&C file on Martin Luther King -- but only a 164-page summary of the rest (e.g., a 1971 memo regarding an unfortunate FBI employe, evidently female, "who was seen by Mr. Hoover and Mr. Tolson in elevator wearing large wig . . . . Mr. Tolson recommended transfer to Identification Building. Mr. Hoover wrote 'Yes' . . . . Miss [deleted] advised to report there first thing 'tomorrow morning.' ").

Unfortunately, there is no "master list" of all the files the FBI has released over the years -- no way to tell, for example, that its records about the Irish Northern Aid Committee, which were retired from the stacks in 1980 because of lack of interest, are still available for inspection.

"If someone is interested in a subject, they can make a written request for it," says Near, who is also in charge of one of the three FBI initial processing units that handle such inquiries. "Many are first-party requests [people asking for FBI records about themselves]. Those could not be released to the general public so there's no [overall] listing."

But if the documents you want have been publicly released before, even if they're not in the stacks, you can have them carted down to the Reading Room. Vernita Turner, the receptionist, will lead you to the tomes and show you how to make out the forms to buy any copies you want. At the FBI, the price is still just 10 cents a page. By contrast, in Kansas City, Mo., where Pretty Boy Floyd is still remembered for the 1933 machine-gun "massacre" of five men at Union Station, records at the U.S. courthouse cost five times as much.

The most recent addition to the Reading Room is the file on Huey Long, the politician who dominated Louisiana in the 1920s and '30s and who had his eye on the White House when he was shot down in the state Capitol at Baton Rouge in 1935. The first entry is about a brouhaha in New Orleans in August 1934, midway through President Franklin D. Roosevelt's first term. Then a U.S. senator, Long was apparently facing stiff opposition to some of his machine's candidates, and he allegedly conspired to have the National Guard take over the Registrar of Voters office with machine guns. Several New Orleans citizens, meanwhile, were complaining that their names had been illegally removed from the registrar's rolls.

The incident is all the more interesting in light of the audience the FBI chose for that report: Marvin H. McIntyre, one of FDR's top aides at the White House. J. Edgar Hoover's penchant for feeding political intelligence to the White House, it appears, began quite early in the history of the FBI.