Terrorist strikes from the sea could be even more catastrophic than those from the air, intelligence officials say. They fear a hijacked oil tanker could be rigged with explosives or a radioactive dirty bomb could be smuggled ashore in a shipping container.

But almost 5,000 ships and about four out of every five of the nation's ports, ferry terminals and fuel-chemical tank farms failed to meet a Wednesday deadline for submitting security plans showing how they will deal with those potential threats.

Security measures to prevent attacks at seaports and inland waterways have fallen far behind efforts to protect airports and airplanes since the 2001 terrorist attacks.

Congress last year ordered the maritime shipping industry to tighten security amid fears that an attack on a port could kill thousands, cause tremendous property damage and cost tens of billions of dollars in lost revenue to the U.S. economy.

Coast Guard officials said the deadline for submitting the plans was met by about 5,200 of 10,000 ships told to submit them and only 1,100 of 5,000 port facilities — despite a potential fine of $25,000.

"We do not have all the plans," Lt. Cmdr. Jeff Carter said. "We recognize that despite our best efforts, there are those who won't comply for a variety of reasons."

Wednesday also was the deadline for airports to start screening all airline baggage electronically for explosives. But Deputy Homeland Security Secretary James Loy told Congress two months ago that the deadline would not be met at five airports.

"A handful" of airports still don't have the screening equipment installed, said Darrin Kayser, a Transportation Security Administration (search) spokesman.

In the aftermath of the Sept. 11, 2001, attacks, Congress required the electronic screeners to be in place a year ago. But when it became clear it couldn't be met, lawmakers moved the deadline back a year.

One reason ships, ports and other facilities were missing their deadline is they were given too little time, said Maureen Ellis, a spokeswoman for the Association of American Port Authorities (search). The government didn't finalize what it wanted until Oct. 22, though the industry was told July 1 they had six months to submit the plans.

Ellis also said some ports found the regulations and requirements to be "overwhelming." The "plan review approval form" for cruise ship terminals, for example, is 20 pages long.

The new law requires a difficult attitude adjustment, said Thomas Allegretti, president of the American Waterways Association (search), which represents owners and operators of tugboats and barges. It's hard for tugboat captains, used to worrying about running aground, to suddenly start thinking about a terrorist hijacking a tanker and using it to inflict damage, he said.

The tugboat and barge industry submitted plans to the Coast Guard that include training crews about potential threats, securing vessels' perimeters and restricting access to vessels, Allegretti said.

Lt. Cmdr. Richard Teubner said the Coast Guard expects to get plans in the mail next week from many ports, stevedoring companies, offshore oil drillers and ship owners.

The plans have to be implemented by July 1, when the Coast Guard can start turning away ships and shutting down ports that don't comply.

James Carafano, a homeland security expert with the Heritage Foundation (search), thinks major ports will meet the July deadline. Otherwise, he said, "the economic consequences are too horrifying to contemplate."

For others, finding the money for fences, guards, lights or closed-circuit TV will be difficult, Ellis said.

"It's one thing to come up with a plan to see what you need to do, but it's a whole other issue how it's going to be paid for," she said.

The General Accounting Office (search), Congress's investigative arm, agrees that paying for the security upgrades will be a challenge.

"Where the money will come from to meet these funding needs is not clear," the congressional auditors said in a Dec. 15 letter to Sen. Ernest Hollings, D-S.C.

As one example, the new regulations require more than 4,000 U.S. ships to install transponders that transmit a signal, giving port officials early warning of an unidentified vessel. But only a handful of ports have the money for installing the equipment to receive the signals, the GAO said.

The Coast Guard estimates that meeting the new requirements will cost $7.4 billion over the next decade.