It was 8:35 a.m. and a voice was barking urgently over the two-war radio: "Alligator at Tamiami Airport. Six-foot alligator blocking runway 11B."

Within seconds, Roy Martinez, alligator catcher, was speeding his state patrol car northward. Normally, he is a state game warden, but this time of the year he spends 70 per cent of his time hunting alligators, not long ago thought in danger of extinction, in this urban area of 1.3 million.

For "urban alligators" as they are called, have become a major pest problem here and in other Florida cities. Last year alone, the state Game and Fresh Water Commission received 10,000 complaints of nuisance alligators in residential canals, roads, swimming pools, golf courses and backyards.

The alligators, ranging in length from one foot to 12 feet, usually cause more fear and curiosity than real dangers. This day, for example, the control tower at the airport spotted a gator lazily moving across a runway about 8 a.m. It promptly shut the runway down and reported the sighting.

But by the time Martinez and two other game wardens arrived, it was nowhere to be seen. They called in a helicopter, which buzzed over a huge pond at the end of the runway. Then, armed with snares and fishing poles, they walked a series of canals which surround the airport. There was no sign of the alligator anywhere.

"This is another story of the alligator that got away," Martinez declared after an hour.

That's how most of Martinez' alligator hunts end. For the alligator, one of the last survivors of the dinosaur age, moves deceptively fast, often travelling up to 25 miles a day.

In large part, the advent of the urban alligator is an environmental success story. Twenty years ago, when conservationists feared that the animal was heading toward extinction after decades of indiscriminate slaughter, there were far fewer sightings in urban areas.

But as result of tough conservation moves, and bans on the sale of alligator hides, the alligator population has grown to more than 500,000 in Florida. And last winter, the federal Interior Department removed them from the endangered species list, reclassifying most of them under the less restrictive "threatened" category.

The comeback of the alligator, which was first put under federal protection in 1966, has received widespread support here. The reptile is considered essential to the life cycle of the Everglades, a swampy wilderness. Deer and other creatures depend on gator holes in time of drought. And their presence is thought to help sport fishing because gators devour trash fish such as gar that would otherwise crowd out bass and bream.

The urban alligator is a different question. Most of them are commuters. "They come out of the Everglades in the mating season and swim into canals looking for mates," said Martinez. "You'd be surprised how many reports we get from the middle of downtown."

The canals, which honeycomb Miami and other Florida cities, form a virtual water freeway into residential and commercial areas.

Many longtime residents don't mind having a friendly alligator around. Some, in fact, have adopted them as neighborhood pets, feeding them leftovers. "Everyone says they like alligators, except in my backyard or canal where they might eat my French poodle, said Donald Ashley, deputy chief of enforcement for the Florida game commission.

It is northerners, who complain most about gators. "A lot of people are unfamiliar with Florida wildlife," added Ashley. "It takes them back when they go out in their backyard and see a six-foot alligator sunning himself on the patio."

There have been few actual alligator attacks on humans. They make for scary reading, However. Mark Ditinick, 19, for example, said he was fishing for sea trout in the India River when he spotted a five-foot gator.

"He lunged for my stomach, just like a spring, and all I saw were those giant jaws and that wide open mouth," he recalled. ". . . I jumped back and he missed. I started screaming and yelling, but I was too far out for anyone to hear me. That mouth was so big coming at me. I'll never forget it."

Ditinick threw his fishing rod at the reptile and ran.The gator lay there watching.

Conservationists fear reports of the expanding alligator population might lead to a change in their status as protected wildlife. Currently, the sale of alligators hides and products is banned in the United States, and open hunting for alligators is allowed only in three Louisiana parishes.

Conservationists blame the increasing number of complaints about urban alligators on the encroachment of humans on the reptiles' natural habitats. "What's actually happening is real estate developers keep eating up more and more swampland and alligators have nowhere to go," said Lewis Regenstein, executive director of the Fund for Animals. "The complaints aren't an indication of an expanding alligator population. It's an indication that their natural habitat is being destroyed."

"The alligator is still an endangered species," he added. "They're just hangling on by a thread in many areas."

Meanwhile, the job of policing the urban alligator is left in the hands of game wardens like Martinez. They have to catch the alligators, often weighing over 200 pounds, wrestle them into the trunks of their cars and cart them back to the Everglades.

How do they do it?

"Very, very carefully," he answered with a wry smile.