Since the September 11 terrorist attacks U.S. authorities have asked the public to be vigilant for possible terrorist activity and to report anything that looks suspicious. Law enforcement officials in south Florida are again enlisting ordinary Americans in the effort to boost security along the region's coastline.

South Florida's seaports, marinas, and waterways are among the busiest in the nation; teeming with tankers, cruise ships, pleasure craft and other vessels. For decades, authorities have battled to keep illegal narcotics and illegal immigrants from reaching south Florida's shores.

Now, law enforcement officials have a new focus: terrorism. Some analysts say the next terrorist threat to the United States may not come from hijacked planes flown into buildings, but from nuclear, chemical or biological materials smuggled into the country, possibly through the nation's seaports.

Florida's state director for homeland security, Steve Lauer, says this challenge cannot be met without the participation and cooperation of the American people.

"Prevention is the number one responsibility of our government, to prevent another terrorist attack," he said. "Terrorism is about murder. It is right that we involve American citizens in our efforts to protect them. None of this can be successful, none of us can be safe, without the active involvement and participation of our citizens."

Hence, "Operation On Guard," a cooperative effort between federal and state authorities to enlist he public in monitoring seaports and waterways for possible terrorist activity. Boaters are encouraged to be on the look-out for suspicious individuals transporting cargo, loitering, renting watercraft, or photographing or making sketches of marine facilities.

Kelly Darden, assistant chief of the FBI's Miami field office, says, above all, people should trust their instincts and keep a watchful eye for anything that seems out of the ordinary.

"It is, indeed, incumbent upon each and every one of us to be vigilant [and] to pass on information that we believe is not quite right (suspicious activities)," he said. "Often we have heard people after the fact say, 'You know, I observed and noticed something, and I knew it was not right.' But they did not pass it on [to authorities]. This initiative allows people to pass on information so that we may act upon it."

At marine facilities across south Florida, hundreds of signs have been posted with a telephone number boaters can call to report suspicious activity. Coast Guard Captain James Watson says the goal is to make sure that tip-offs from the public get to the proper law enforcement officials.

"We have had a lot of people call in on our search-and-rescue radio frequency and to the 911 (emergency) operators in a very disorganized way, and often the wrong operator is getting information for the particular situation at hand," he said. "This [initiative] brings some order to what is already happening."

The director of south Florida's Marine Industry Association, Frank Kerhold, says boaters can be of great help in the fight against terrorism.

"There are about 400,000 boaters from Palm Beach to Key West, which is the 'On Guard' section," he said. "To some extent, we are the first line of defense. Our people are out in the ocean; they are in the ports. The family recreational boater may be the first to notice when something is out of order or out of line."

But not everyone thinks Operation On Guard is a good idea. Civil rights activists say there is a fine line between asking the public to be vigilant and encouraging people to spy on one another - the latter of which, they argue, is more reminiscent of a police state than an open society where civil liberties are protected.

Captain Watson says such fears are unwarranted.

"The public is not (to be used as) spies. We are talking about public areas here, nowhere near anybody's home," he said. "What we are doing is very much like what we did in World War II: we enlisted the support of the boating public to monitor the coast. In those days, for U-boats; in these days, for activity that could be terrorism-related."

But even Captain Watson admits that, for Operation On Guard to succeed, boaters must exercise good judgement and discern between harmless activities and those that could truly pose a threat.

"It would not be unusual for people to be taking pictures or sketching out on Miami Beach," he said. "It would be unusual if someone did repeated photography of the port in a way that is clearly not like a tourist."

Operation On Guard targets south Florida's busy coastline. Similar programs are being instituted along waterways elsewhere in the nation.