Larry Walters is a man who knows the meaning of "fly now--pay later."

In July, the 33-year-old Californian made headlines when he strapped himself into a $100 Sears aluminum lawn chair, tied 45 helium balloons to its sides and ascended 16,000 feet before returning safely to earth.

"It made America laugh," Walters said yesterday.

But the Federal Aviation Administration isn't laughing. In fact, the government agency has just slapped Walters with a $4,000 fine, saying he violated four FAA regulations: operating an aircraft for which there is no "airworthiness certificate," flying too close to Long Beach Airport, not maintaining contact with air traffic controllers and operating his chair-craft "in a reckless and careless manner."

"The charges are a bunch of ----," Walters said yesterday, reached at his North Hollywood home. "I can prove my innocence."

The former truck driver-turned-celebrity said yesterday he spent 20 years preparing for the flight, which took place last July 2 from his girlfriend's San Pedro, Calif., back yard.

Why the lawn chair? "I wanted to be comfortable," he said.

Wearing a parachute and carrying two citizens' band radios, Walters shot three miles into the air and was spotted by two startled jetliner pilots. (Walters said yesterday he never saw the jetliners, but did pass a few private planes on his way up.)

After 90 minutes, he shot out 10 of the balloons with a BB gun. But the gun fell overboard at 15,000 feet, and the chair drifted to earth, controlled only by jugs of water attached to the chair as ballast. Walters landed safely, after his ropes became entangled in a power line and briefly blacked out a small area of Long Beach. The lawn chair dangled five feet above the ground and Walters hopped out.

"I did something that was very American," he said. "The flight has inspired a lot of people."

Walters said he was in constant contact with his ground crew and that tapes of the flight, dubbed "The Inspiration," will vindicate him of all charges. He called the experience "exhilarating, almost intoxicating . . . I knew what I was doing at all times. I had complete control of my aircraft. The fact is, it created no havoc."

Walters said he originally planned to spend 15 hours aloft, hoping to travel 300 miles and land in the Mojave Desert.

A spokesman for the FAA's West Coast office said it was the first time the government agency had ever gone after a lawn chair.

"It wouldn't have been so funny if he'd interfered with an air carrier, said spokeswoman Barbara Abels.

Each of the four violations carries a fine of $1,000. "The bottom line is the FAA will be unwilling to settle for less than $4,000," Abels said.

"They're doing it to set an example," Walters countered yesterday, "so every Tom, Dick and Harry won't take up their toilet bowl or lawn chair."

But what goes up must come down.

After appearing on the David Letterman Show and turning down $100,000 from a San Diego concern to repeat the performance ("I wouldn't do it illegally again"), Walters said yesterday he left his job as a truck driver three months ago and since has declared bankruptcy. "This thing broke me," he said. "A lot of people think I landed on money bags."

Still, he said, two people already have offered to pay the $4,000 fine for what he called his "fantasy flight." And Walters is scheduled to appear on a nationwide radio show next week "to take my case to the American people."

"It's a land of plenty," he said, "even for retired lawn-chair pilots."