Dozens of terror suspects on federal watch lists were allowed to buy firearms legally in the United States last year, according to a Congressional investigation that points up major vulnerabilities in federal gun laws.People suspected of being members of a terrorist group are not automatically barred from legally buying a gun, and the investigation, conducted by the Government Accountability Office (GAO), indicated that people with clear links to terrorist groups had regularly taken advantage of this gap.Since the September 11 attacks, law enforcement officials and gun control groups have voiced increasing concern about the prospect of a terrorist walking into a gun shop, legally buying an assault rifle or other type of weapon and using it in an attack.The GAO study offers the first full-scale examination of possible dangers posed by gaps in the law, Congressional officials said, and concludes that the FBI ‘‘could better manage’’ its gun-buying records in matching them against lists of suspected terrorists. FBI officials maintain that they are hamstrung by laws and policies restricting the use of gun-buying records because of concerns over the privacy rights of gun owners.At least 44 times from February 2004 to June, people whom the FBI regards as known or suspected members of terrorist groups sought permission to buy or carry a gun, the investigation found. In all but nine cases, the FBI or state authorities who handled the requests allowed the applications to proceed because a check of the would-be buyer found no automatic disqualification like being a felon, an illegal immigrant or someone deemed ‘‘mentally defective’’, the report found.In the four months after the formal study ended, the authorities received an additional 14 gun applications from terror suspects, and all but two of those were cleared to proceed, the investigation found. In all, officials approved 47 of 58 gun applications from terror suspects over a nine-month period last year, it found.The gun buyers came up as positive matches on a classified internal FBI watch list that includes thousands of terrorist suspects, many of whom are being monitored, trailed or sought for questioning as part of terrorism investigations into Islamic-based, militia-style and other groups, official said.GAO investigators were not given access to the identities of the gun buyers because of those investigations. The report is to be released on Tuesday, and an advance copy was provided to The New York Times.Senator Frank R. Lautenberg, Democrat of New Jersey, who requested the study, plans to introduce legislation to address the problem in part by requiring federal officials to keep records of gun purchases by terror suspects for a minimum of 10 years. Such records must now be destroyed within 24 hours as a result of a change ordered by Congress last year. Lautenberg maintains that the new policy has hindered terrorism investigations by eliminating the paper trail on gun purchases.He blamed the Bush administration’s ‘‘twisted allegiances’’ to the National Rifle Association (NRA) for the situation. The NRA and gun rights supporters in Congress have fought—successfully, for the most part—to limit the use of the FBI’s national gun-buying database as a tool for law enforcement investigators, saying the database would amount to an illegal registry of gun owners nationwide.FBI officials acknowledge shortcomings in the current approach to using gun-buying records in terror cases, but they say they are somewhat constrained by gun laws as established by Congress and interpreted by the Justice Department.The report concluded that the FBI should keep closer track of the performance of state officials who handle gun background checks in lieu of the FBI.