The CIA is to release hundreds of pages of secret files describing its illegal assassination attempts, wiretappings, kidnappings and behaviour experiments between the 1950s and 1970s.

A 693-page document describing the agency's so-called "family jewels" was compiled in the aftermath of the Watergate scandal, when it was revealed that former CIA officers had helped President Nixon carry out "dirty tricks" against his political opponents.

The then-CIA director, James Schlesinger, sent a letter to every employee of the agency to report all activities that they knew about that "may have fallen outside the CIA's charter".

The result was information on hundreds of incidents — including the detention of a suspected Russian spy for two years and attempts to kill Fidel Castro — whose disclosure Henry Kissinger, then US Secretary of State, warned would have heavier consequences than the scandal that caused the inquiry in the first place.

Announcing last night that the file would be released next week, the current CIA director, Michael Hayden said: “Much of it has been in the press before, and most of it is unflattering, but it’s the CIA’s history." Many of the events described in the papers are already known, but the official versions have never been seen.

Mr Hayden, who has made a conscious effort to separate America's senior intelligence agency from a recent inglorious past that includes failures surrounding the September 11 attacks, the invasion of Iraq and allegations of the illegal wiretapping of US citizens, said the documents showed “a very different time and a very different agency".

“This is about telling the American people what we have done in their name."

Ahead of the full publication of the "family jewels" and a further 11,000 pages of CIA memos, mainly about Soviet and Chinese internal politics and Warsaw Pact military programmes, the National Security Archive at George Washington University last night released a series of other documents describing their contents.

One memo was an account of a conversation between William Colby, Mr Schlesinger's successor at the CIA, and President Gerald Ford in January 1975 about "allegations of CIA domestic activities" that took place shortly after The New York Times revealed details of an illegal wiretapping programme of 9,900 Americans uncovered by the internal inquiry.

"I think we have a 25-year-old institution which has done some things it shouldn't have," Mr Colby told President Ford, before outlining details of the secret eavesdropping of American anti-war dissidents and leftists and the opening of post sent from the USSR and China.

"We did have a New York and Los Angeles programme in the 1950's of opening first-class airmail from the USSR. For example we have four to Jane Fonda," he said. "That is illegal, and we stopped it in 1973."

Mr Colby was giving President Ford a summary of a fuller briefing given by the CIA to the Department of Justice in late 1974 about its "skeletons". That briefing, also released last night, contained 18 specific illegal acts that the agency shared with government lawyers.

These included the surveillance of journalists, including the celebrated muckraking columnist, Jack Anderson and one his reporters, Brit Hume, who is currently an anchor on Fox News. The CIA also admitted into breaking into the homes of its employees and former defectors looking for classified documents.

The briefing also described the detention of a Soviet defector, considered a "fake" by the CIA, who was locked up and interrogated for two years in Virginia. "Colby speculated that the confinement of the Russian defector from 1964 to 1966 might be regarded as a violation of the kidnapping laws," the memo said.

Among the secrets recognised as highly incendiary in the early 1970s were those concerning the CIA's involvement in attempts to kill foreign leaders.

In a memo dated January 3, 1975, Mr Kissinger warned that "blood will flow" if certain information leaked out: "For example, Robert Kennedy personally managed the operation on the assassination of Castro," he said, referring to President Kennedy's younger brother, the US Attorney General from 1961 to 1964.

The "family jewels" include CIA operations aimed at killing Castro as well as Rafael Trujillo, the Dominican dictator, and Patrice Lumumba, the first elected Prime Minister of Congo who died in mysterious circumstances after being arrested by rivals and Belgian officers in 1961.

But, according to the briefing given to the Department of Justice in 1974, the agency "had no role whatsoever" in the murder of Lumumba and only "faint connections" to the men who gunned down Trujillo, also in 1961.

Historians will hope that the files also shed light on some of the more esoteric activities of the CIA, such as research into "behaviour modification" carried out by the agency on members of the public "on an unwitting basis" in some American universities. One experiment described by Mr Colby had participants being observed as they approached a pole erected in the middle of a pavement and seeing which way they passed by.

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