Congressional investigators testing U.S. port security smuggled enough radioactive material into the United States last year to make two radiological "dirty" bombs, officials told a Senate panel yesterday.

In December, undercover teams from the Government Accountability Office, Congress's audit arm, carried small amounts of cesium-137 -- a radioactive material used for cancer therapy, industrial gauges and well logging -- in the trunks of rental cars through border checkpoints in Texas and Washington state. The material triggered radiation alarms, but the smugglers used false documents to persuade U.S. Customs and Border Protection inspectors to let them through with it.

"These are documents my 20-year-old son could easily develop with a simple Internet search," said Sen. Norm Coleman (R-Minn.), who chaired the hearing into covert nuclear threats before a Senate Homeland Security and Governmental Affairs subcommittee yesterday. "It is a problem when it is tougher to buy cold medicine than it is to acquire enough material to construct a dirty bomb."