It's the first time the FBI has publicly acknowledged the high risk to the state ferries system. The findings are based largely on analysis of suspicious incidents at the nation's maritime centers.

"Our conclusion was that there was an extremely high likelihood, in a handful of incidents, that there was pre-operation planning" for a terrorist attack on the ferry system, said supervisory intelligence analyst Ted Turner of Seattle's FBI office.

Washington's ferry system and Gulf Coast fuel tankers were considered the No. 1 targets.

Turner and other local FBI officials, along with the Coast Guard, said Thursday that the attention Washington's ferry system has drawn may be because of more aggressive reporting in this region.

The FBI compiled reports on 247 suspicious incidents involving the ferry system between April 2004 and September 2005, an increase from the 157 incidents documented between Sept. 11, 2001, and April 2004.

"You cannot conclude from the fact that we have a lot of intelligence reporting that we are a No. 1 target," said Laura Laughlin, the FBI's special agent in charge in Seattle. "Obviously, the potential for a terrorist incident is here. But that's reading a lot into it to say that."

There have been fewer incidents considered high-risk in the most recent reporting period, Turner said.

"We've never been able to tie a specific incident to a terrorist group," he said. "We've never been able to tie a specific incident to a terrorist plan."

Each year Washington State Ferries carries more than 26 million passengers to 20 different ports in Washington and British Columbia, Canada.

At Seattle's Colman Dock, which serves more than 9 million ferry passengers a year, the state has proposed a $225 million project to build a new terminal and possibly a hotel or office space. The remodel would include expanded passenger access from the terminal to the ferries, said Tim King, with the ferry system.

After the FBI's Seattle office in May 2004 released assessments of potential threats to the ferry system, bomb-sniffing dogs were introduced, unaccompanied freight was eliminated and additional surveillance equipment was added. State Patrol troopers also began riding the ferries, accompanied in the water by heavily armed Coast Guard SWAT team boats.

Security enhancements have gone into effect in the last couple of years, and the measures are being continuously re-evaluated, said Coast Guard Capt. Stephen Metruck, who oversees maritime operations in Puget Sound.

For the seaport-protection report, the FBI's Threat Monitoring Unit identified all maritime-related suspicious incidents reported from September 2004 to September 2005.

There were 51,000 suspicious incidents reported. The FBI identified the 68 most significant maritime-related incidents, with the greatest concentration in the Seattle area, the report states.

Of the 68, 46 were considered to be acts of surveillance by terrorists.

Nearly half the suspected maritime targets nationally were terminals and ferries, and both were "frequently filmed or photographed in the Seattle area by people acting suspiciously," the report said.

Neither the local FBI office nor the Coast Guard would discuss specific incidents.

The report noted "a substantial number of threats along the Gulf Coast, which most likely involved suspected surveillance of energy facilities and oil tankers."