Finding biological and chemical weapons inside cargo containers is less likely. The study said tests were "labor intensive, time-consuming and costly to use" and produced too many false alarms. "No silver bullet has emerged to render terrorists incapable of introducing WMD into containers," it said.
Sen. Patty Murray, who advocated the study, said: "There are huge holes in our security system that need to be filled." The Washington Democrat said the study "shows us there are major vulnerabilities over who handles cargo, where it's been and whether cargo is on a manifest."
Part of the study tested new tamper-evident locks on containers and tracking devices.
"It's important to figure out what works and what doesn't," said Elaine Dezenski, Homeland Security's acting assistant secretary for policy development. She said the study "gave us a much better view of vulnerabilities." The U.S. is looking for weaknesses across the shipping system to learn where terrorists might strike, she said.
The study, called "Operation Safe Commerce," undercuts arguments that port security in America is an exclusive province of the Coast Guard and U.S. Customs and Border Protection and is not managed by companies operating shipping terminals.
The theme was an important element in the Bush administration's forceful defense of the deal it originally approved to allow Dubai-owned DP World to handle significant operations at ports in New Jersey, Baltimore, New Orleans, Miami and Philadelphia.
Bush and senior officials sought to assure lawmakers that safety at ports would not decline.
"I can understand people's consternation because the first thing they heard was that a foreign company would be in charge of our port security when in fact, the Coast Guard and Customs are in charge of our port security," Bush said Feb. 28. "Our duty is to protect America, and we will protect America."
DP World promised on Thursday to transfer fully to an American company its U.S. port operations it acquired when it bought London-based Peninsular & Oriental Steam Navigation Co.
It was unclear how such a sale might occur, but the divestiture was expected to involve major operations at the six U.S. ports and affect lesser dockside activities at 16 other ports in this country.
Sen. Robert Menendez, D-N.J., a leading critic of the Dubai deal, said anyone suggesting that port operators and shipping companies were not involved with security was "living in La-La land."
"You can obviously have stuff in containers that doesn't make it onto manifests, either by design or from the actions of bad actors," Menendez said in an AP interview Friday. "A terminal operator is so involved in the overall security equation of ports."
Parts of the U.S. study examined the safety of containers sent to the same cargo terminal in New Jersey that DP World would have managed jointly and operated with its Denmark-based rival, Maersk Sealand.
Hundreds of pages of study documents obtained by the AP do not list specific security lapses at the New Jersey terminal. The final two cargo containers being tracked under the study were expected to arrive there this week from the Middle East.
But the study broadly described problems in warehouses and other storage areas that raised doubts about the safety of containers brought to New Jersey's port. It cited problems with protective fences and gates, surveillance cameras and emergency plans.
The lengthy study has been beset by problems. Japan refused to allow officials to attach tracking devices to containers destined for the United States. Other tracking devices sometimes failed. Many shipping companies refused to disclose information for competitive reasons.
Some containers in the study were aboard a ship the Coast Guard held 11 miles off New Jersey's coast for security reasons in August 2004. An anonymous e-mail had claimed a container filled with tons of lemons was deliberately contaminated with a biological agent. The lemons were fumigated and burned, but no trace of poison was ever found; the containers also were destroyed.
Parts of the study could not be finished at all. U.S. officials went to Pakistan to inspect how workers in Karachi handle cargo containers. But they canceled plans for a return inspection because of an outbreak of terrorist attacks there.