WASHINGTON, Sept. 7 - Senator Bob Graham, the Florida Democrat who is a former chairman of the Senate Intelligence Committee, accused the White House on Tuesday of covering up evidence that might have linked Saudi Arabia to the Sept. 11 hijackers.

Mr. Graham made the accusation in a new book and repeated it at a news conference Tuesday arranged by Senator John Kerry's presidential campaign. Republicans called the accusations "bizarre conspiracy theories," and the Saudis said they were unsubstantiated and reckless.

The accusation stems from the Federal Bureau of Investigation's refusal to allow investigators for a Congressional inquiry and the independent Sept. 11 commission to interview an informant, Abdussattar Shaikh, who had been the landlord in San Diego of two Sept. 11 hijackers.

In his book "Intelligence Matters," Mr. Graham, the co-chairman of the Congressional inquiry with Representative Porter J. Goss, Republican of Florida, said an F.B.I. official wrote them in November 2002 and said "the administration would not sanction a staff interview with the source." On Tuesday, Mr. Graham called the letter "a smoking gun" and said, "The reason for this cover-up goes right to the White House."