PORTLAND – Erring on the side of caution, law enforcement officials shut down the four-lane Casco Bay Bridge twice Wednesday after a threat was overheard on a marine radio channel.

The bridge was shut down for five hours at 12:28 a.m. and then again for 30 minutes in the afternoon because the threat specifically mentioned something happening at 12:59 p.m.

The radio message intercepted by the Coast Guard featured a woman’s voice talking about the destruction of the bridge, officials said.

FBI Special Agent James Osterreider said law enforcement agencies decided to err on the side of caution even though the FBI officials who reviewed the tape said they were leaning toward declaring it a hoax.

During the second shutdown, camouflage-clad officers equipped with automatic weapons patrolled the bridge on foot while uniformed police officers and a bomb-sniffing dog swept the area under the bridge.

Air traffic was shut down and a Coast Guard helicopter hovered overhead. Coast Guard vessels also patrolled the waters.

Todd Hutchins, who was stopped from walking across the bridge to his home in South Portland, expressed skepticism.

“Honestly, I think they’re crying wolf too many times with this orange alert and warnings,” Hutchins said. “I understand the need for security but they’re making us immune to it.”

But most pedestrians and motorists praised law enforcement authorities for taking the threat seriously.

“I’d rather be safe than sorry,” said Todd Hoyt, who wasn’t allowed to drive under the bridge on Commercial Street.

“I think they’re doing a good job. It’s fantastic the way they’re handling it,” said Ron Vezina, a construction worker. “I’d rather be inconvenienced than to have something happen.”

The Coast Guard overheard the woman’s voice over VHF Channel 16, a maritime channel, officials said.

The bridge was closed shortly thereafter. Officials conducted a thorough search of the bridge overnight but found nothing suspicious. It was reopened around 6 a.m., in time for the busy morning commute.

The bridge was closed again from 12:45 to 1:15 p.m., a period that included the 12:59 p.m. mentioned in the threat.

Portland police Chief Michael Chitwood, who was critical of the FBI for not sharing information after the Sept. 11 terrorist attacks, said the incident demonstrated that cooperation has improved.

“That’s proof that things have changed and that working relationships are very good,” the chief said.