A huge blimp-like balloon floating serenely in the southern Arizona sky is a new weapon in a widening war, a radar-packed eye-in-the-sky searching for airborne drug smugglers.

When it becomes fully operational this month, the nearly $18 million balloon will scan the sky to the south, tracking low-flying planes that try to evade regular radar, and helping U.S. Customs Service aircraft chase smugglers within 80,000 square miles.The helium-filled, white balloon already has tracked planes twice, leading to arrests and seizure of drugs, said Daniel Wiley, senior engineer and site manager for the contractor, Westinghouse Defense and Electronic Systems Co.

It is the first of at least five balloons Customs officials hope to position along the southwest border to plug gaps in ground-based radar surveillance that have allowed smugglers to enter the country with impunity via Mexico.

Some residents near the giant balloon's mooring on the southern edge of the Fort Huachuca military reservation say they're worried that it poses a danger to them.

"I'm sure the government's going to leave it there until it has an accident, and then things will change. And it ultimately will have an accident," said Harry Woodward, whose home is within the radius of the balloon's 10,000-foot-long tether.

Within the balloon's range are 1,000 homes, five churches and Huachuca Mountain Elementary School, where Carol Southland, a second-grade teacher, is among those who appreciate its deterrent role in the war on drugs.

"I just don't think the risk is there," she said. "I don't think the balloon's gonna run away through the neighborhood and carry off the children."

Army and Customs officials say the site was the best available and fears of an accident are unfounded.

The balloon has a rapid deflation device to allow operators to lower it quickly while controlling where it lands if it were to break from its tether.

Sabotage would be the most likely cause of a breakaway from the mooring, but it would be a difficult target for anything but a rocket, Wiley said.

Because of the helium's low pressure, "you could put probably a dozen (bullet) holes in this Aerostat out here and it would probably take us days to even find out we had a leak," he said.

The balloon goes by various names: Aerostat (for air stationary) Borne Radar Surveillance System; SOWRBALL (Southwest Radar Balloon); "Fat Albert," and even "Little Shamu," after the whale of Sea World fame.

At 245 feet long and 72 feet in diameter, it dwarfs a Boeing 747. It weighs 12,750 pounds, including the 3,500-pound down-looking radar payload strapped to its underbelly.

But its eight-layered skin is puff-pastry thin - at 12 mils, or 12-thousandths of an inch, it's about twice the thickness of the tape in an audio cassette.