CHATTANOOGA, Tenn. (AP) _ It began as a spur-of-the-moment spoof, a lighthearted jab at Chattanooga's upper crust and their yearly social gala, the Cotton Ball.

But the Kudzu Ball, showing a tenacity its leafy little namesake would be proud of, has slowly become an annual event in its own right in this Tennessee river town.

''People just like to get out and have a good time,'' L.R. ''Tex'' Greenwood, one of the ball's founders, said Thursday. ''It's inexpensive, it's for a good cause. And it gives people a chance to act like a bunch of kids. It's just fun.''

The seventh annual Kudzu Ball, complete with its own king and queen, bluegrass bands and a best-costume contest, is set for tonight at the Town and Country Shopping Center in North Chattanooga.

Well, not exactly the shopping center itself - the parking lot outside JB & Friends, a night spot where the idea was hatched for a kooky celebration of the South's most famous weed.

''A group of pseudo-intellectuals was sitting there one night, and we decided that to quaff 'em once or twice a week, we needed a purpose,'' said Greenwood.

''Somebody said, 'Let's have a ball.' And one of us looked out the window, and there was kudzu all over this hill next to the bar, and someone said, 'How about a kudzu ball?'''

Kudzu, as any Southerner worth his grits knows, is the Oriental vine introduced to Dixie 50 years ago to stop soil erosion. The problem was that the pesky little weed didn't know when to stop.

It's been known to grow a foot overnight and has proven impervious to most efforts to kill it. Today, the creeping, choking vine blankets seven million acres in 12 southeastern states, not to mention telephone poles, cars, houses and lazy dogs who snooze in one place too long.

All of which made it the perfect inspiration for an offbeat ball that's always been held the same night as the more socially polite Cotton Ball, itself named for the South's other famous plant.

Greenwood admits the organizing group, known as the Long-Range-Way-Down- the-R oad-and-Out-of-Sight Planning Commission, may have had an assist from the Swine Ball, Nashville's takeoff on its own Swan Ball.

But the Kudzu Ball has taken on an identity of its own, drawing 5,000 to 7,000 people a year into the cozy little parking lot, many of them festooned with snips of the wily weed.

''They like to be like the kudzu itself - all cluttered up and close together, like a bunch of sheep,'' Greenwood said.

Tickets are $5 each - the event has raised about $43,000 for the Chattanooga Birth Defects Center over the years - but organizers say some of the costumes alone are worth that price.

You might see a green-tinted dog with a sign reading ''Kudzu MacKenzie,'' or a rugged, bandoleer-and-kudzu-draped commando calling himself Kudzo.

Greenwood routinely shows up as a bandanaed balladeer named Kudzu Willie, and this year's ball promises a debate between Michael Dukudzu and Gorge Bush.

There's plenty of bluegrass music, vendors have been known to sell a beer or two, and the festivities general wind up with the selection of a king and queen from a 12-member court.

It took awhile for the Cotton Ball organizers to get used to the parody celebration. But now, said Greenwood, they've apparently accepted it, since some of the debutantes usually show up at the Kudzu Ball after their event is over.

''Now, we have never been invited to theirs. And I don't think we're going to,'' Greenwood said, chuckling. ''Which I don't blame 'em. I wouldn't ask me in, either.''