PORTLAND – Missiles and munitions trucked around the country by Defense Department contractors were left unguarded because of security lapses that left them vulnerable to theft, a government study ordered by U.S. Sen. Susan Collins has found.

The General Accounting Office study, completed in July, concluded that there were few safeguards to ensure that deadly weapons do not wind up in the hands of intruders.

Undercover investigators gained access to Stinger missiles and cruise missiles by flashing phony identification as Army inspectors, according to findings from the study first reported Thursday in The New York Times.

The missiles were stored temporarily in private trucking terminals while en route to military bases and firing ranges, according to the GAO study.

Collins ordered the study when she chaired the Permanent Subcommittee on Investigations. She had taken steps to release the report just before the attacks on the World Trade Center and Pentagon.

After the attack, the Defense Department moved to classify the documents. Collins’ office was required to collect copies of the report and supporting documents, and turn them over to the military, according to Felicia Knight, spokeswoman for Collins.

Collins will no longer speak about the report, citing national security.

But in an interview with “Primetime,” which was taped just before the attack, she talked about the report and criticized how the weapons were handled. That interview aired Thursday night on ABC.

“L.L. Bean . . . can tell you precisely where every package is that they shipped,” Collins told the show. “But the Pentagon can’t tell you where some of the most dangerous munitions are at any given time, and that’s frightening.”

Some of the weapons, including hand-held rockets, were ready to fire, according to the report. Others could create “explosions that could cost lives and destroy residences and businesses,” the report said.

The Defense Department makes about 40,000 shipments of explosives each year; about one-fifth of the shipments include cruise missiles and hand-held rockets.

According to The New York Times, a separate classified GAO report found that the military often was unaware of the location of weapons being shipped. For example, investigators discovered that a shipment of 192 Stinger surface-to-air missiles was left temporarily in a civilian storage area without the knowledge of either the military or contractor.

Military officials told “Primetime” that identification checks have become stricter since the investigation and the Sept. 11 attacks.

Terminals handling such shipments will be required to have armed guards by the end of the year.