MIAMI - When the FBI investigated the landmark 1972 pornographic movie

Deep Throat

, the case touched the highest levels of the FBI, even its second-in-command, W. Mark Felt, the shadowy Watergate informant whose alias was taken from the movie's title.

The FBI documents newly released to the Associated Press reveal the bureau's sprawling and ultimately vain attempt to stop the spread of a movie that some saw as the victory of a cultural and sexual revolution and others saw as simply decadent.

Agents seized copies of the movie, had negatives analyzed in labs, and interviewed everyone from actors and producers to messengers who delivered reels to theaters.

"Today we can't imagine authorities at any level of government - local, state, or federal - being involved in obscenity prosecutions of this kind," said Mark Weiner, a constitutional-law professor and legal historian at the Rutgers-Newark School of Law.

"The story of Deep Throat is the story of the last gasp of the forces lined up against the cultural and sexual revolution, and it is the advent of the entry of pornography into the mainstream."

The papers are among 498 pages from the FBI file on Gerard Damiano, who directed the movie and died in October. Released this month after a Freedom of Information Act request by the AP, they are just a glimpse into his roughly 4,800-page file.

More than 1,000 additional pages were withheld under FOIA exemptions and because they duplicated other material; the balance of the file has not yet been reviewed and released.

Many parts of the released files are whited out, and the FBI's ultimate targets are unclear, but the seriousness with which the agency treated the investigation is unquestionable.

The file includes memos among the FBI's top men - L. Patrick Gray, William Ruckelshaus, and Clarence Kelley, successive heads of the agency after J. Edgar Hoover - and field offices so widespread, it seemed that nearly all the biggest U.S. cities were involved.

On various entries in the file, a checklist of top FBI brass appears in the top right corner, with initials next to some names. One of those listed is Felt, the FBI second-in-command who became the Watergate informant long known only as "Deep Throat."

None of the markings indicate that Felt read any of the materials on the movie whose name became synonymous with his role in bringing down Richard Nixon's presidency. However, former FBI agents interviewed by the AP after the documents were released said Felt almost certainly would have been aware of the huge investigation.

While much of the probe of the film centered in New York, where many involved in the film lived, and Miami, where it was largely shot, agents from Honolulu to Detroit were involved.

Aside from investigative records tracking subpoenas, interviews, screenings, and shipments of the film, the Damiano file includes various FBI agents' play-by-play accounts of the movie's plot, and the specific role of Damiano in the agency's investigation.

The FBI noted that Damiano had been "somewhat cooperative." On Aug. 7, 1973, an assistant U.S. attorney general wrote to Kelley, saying Damiano was being considered for immunity. The memo did not specify the crime, though mentioned throughout the file is the charge of interstate transportation of obscene material.

Among the areas of the case file whited out is an interview with the star of the film, who at the time went by the name Linda Lovelace.

Deep Throat become the most widely known adult film to reach a general audience. It was hugely profitable and became a cultural buzzword.

Authorities have long said the movie was made with Mafia money - and the FBI has linked the mob with porn over the years - but the file includes no mention of mob links.