ZURICH, May 11 (Reuters) - A Swiss investigation has found no evidence that a former government minister struck a secret deal offering diplomatic assistance to the Palestine Liberation Organization in 1970 in exchange for the PLO halting attacks on Swiss targets.

The allegations emerged this year in a book, "Swiss Terror Years," which also raised questions whether a pact with the PLO had interfered with an investigation into a bomb attack on a Swissair jet in 1970 that killed 47 people.

Carlos the Jackal, the Marxist guerrilla who became a symbol of Cold War anti-imperialism, told a newspaper in March that he moved freely through Switzerland in the 1970s under a "non-aggression pact" between the government and PLO. He is serving life sentences in France for a series of attacks.

In a statement on Wednesday, the government said a task force set up to review the allegations found no indication of a secret pact between former cabinet member Pierre Graber, or any other Swiss representative, and PLO official Farouk Kaddoumi.

"The task force has come to this conclusion: There was no 'secret agreement' reached in September 1970 between F. Kaddoumi and representatives of Switzerland in Geneva," the task force wrote in a 3-1/2 page summary of its conclusions.

The task force - with representatives from the Swiss military, foreign ministry, federal police and justice departments as well as the attorney general and federal archive - also found no evidence that Swiss prosecutors had been obstructed from investigating the air disaster.

The panel reached its conclusions after examining nearly 400 government and police files, Graber's papers and the archives of the International Committee of the Red Cross.

It also obtained written replies from Kaddoumi; Walter Buser, the only participant at cabinet meetings in 1970 still alive; and Pierre-Yves Simonin, then Graber's personal adviser.

Wednesday's report did not address his contentions.

In his book, Swiss journalist Marcel Gyr wrote that Graber, who died in 2003 at age 94, secretly struck a pact with the PLO after attacks including the killing of an Israeli airline pilot in 1969 at Zurich airport and a 1970 incident in which hundreds of hostages on three jets were forced to land in Jordan.

The task force wrote that Gyr declined to provide it with access to anonymous sources he used for his book.

In a written response to questions from Reuters on Wednesday, Gyr said he found the report "fair and substantial" but stuck by his original hypothesis that a secret deal had been forged, based on interviews he conducted with anonymous sources that formed the basis of his book.

"I have always written that there was no definitive written proof," he said.

(Reporting by Michael Shields and John Miller; Editing by Mark Heinrich) ((zurich.newsroom@thomsonreuters.com; +41 58 306 7336;))