Washington ? Undercover investigators slipped radioactive material – enough to make two small “dirty bombs” – across U.S. borders in Texas and Washington state in a test last year of security at American points of entry.

Radiation alarms at the unidentified sites detected the small amounts of cesium-137, a nuclear material used in industrial gauges. But U.S. customs agents permitted the investigators to enter the United States because they were tricked with counterfeit documents.

The Bush administration said Monday that within 45 days it will give U.S. Customs and Border Protection agents the tools they need to verify such documents in the future.

The Government Accountability Office’s report, the subject of a Senate hearing today, said detection equipment used by U.S. customs agents to screen people, vehicles and cargo for radioactive substances appeared to work as designed.

But the investigation, carried out simultaneously at both border crossings in December 2005, also identified potential security holes terrorists might be able to exploit to sneak nuclear materials into the United States.

“This operation demonstrated that the Nuclear Regulatory Commission is stuck in a pre-9-11 mind-set in a post-9-11 world and must modernize its procedures,” Sen. Norm Coleman, R-Minn., said Monday in a statement.

The NRC, in charge of overseeing nuclear reactor and nuclear substance safety, challenged that notion.

“Security has been of prime importance for us on the materials front and the power plant front since 9-11,” commission spokesman David McIntyre said in an interview.

The head of the Homeland Security Department’s Domestic Nuclear Detection Office, Vayl Oxford, said the substance could have been used in a radiological weapon with limited effects.

A Senate Homeland Security subcommittee, which Coleman leads, released details of the investigation and two GAO reports on radiation detectors and port security before hearings on the issues this week.

The GAO, the investigative arm of Congress, also found that installation of radiation detectors is taking too long and costing more money than the U.S. expected. It said the Homeland Security Department’s goal of installing 3,034 detectors by September 2009 across the United States – at border crossings, seaports, airports and mail facilities – was “unlikely” to be met and said the government probably will spend $342 million more than it expects.