All 58 were identified by the FBI as being either known or suspected terrorists and many are being watched or monitored by the agency.

Under current laws, terrorist suspects are not barred from owning firearms. Although background checks are carried out on all firearms purchasers, only convicted criminals, illegal immigrants and the mentally ill are prevented by law from owning guns.

The FBI has complained that laws restricting its use of gun owner records is hampering attempts to bar weapon sales to people regarded as extremely dangerous.

"We're in a tough position,'' an FBI agent told the New York Times. "Obviously we want to keep guns out of the hands of terrorists, but we also have to be mindful of privacy and civil rights concerns, and we can't do anything beyond what the law allows us to do."

Critics of the Bush administration have said that it has put the interests of gun owners before the advice of counter-terrorist officers because of an inbuilt sympathy for weapons enthusiasts. In particular, they pointed out that the former attorney general, John Ashcroft, had for many months prevented the FBI from matching its terrorist watch list against lists of gun buyers on civil liberties grounds.

The report by the Government Accountability Office, which carries out many investigations on behalf of the US Congress, said the FBI should be offered greater powers to bar purchases by terrorist suspects.

The report also revealed that federal agents are legally obliged to destroy the records of weaponry purchases by such individuals within 24 hours, because of privacy laws.

Frank Lautenberg, the Democratic Senator of New Jersey who commissioned the study, blamed the situation on the administration's "twisted allegiances" to the National Rifle Association, America's leading defender of the constitutional right to bear arms.

He said that he would be demanding action from the US government, including an immediate requirement that the FBI keep the weapon purchase records of terrorist suspects for 10 years.

Individuals on the FBI's terrorism watch list - believed to number several thousand - should also be prevented from owning firearms, the senator said.

Peter Hamm, communications director for the Brady Campaign to Prevent Gun Violence, said: "We have been trying to warn the public that the policies of the current administration and some of the legislation passed by Congress is going completely 180 degrees in the wrong direction when it comes to preventing terrorists from arming themselves."