THE HULA HOOP TWIRLS on.

Not in the numbers it once did, of course. In a dizzying first six months on the market in 1958, an estimated 100 to 120 million Hula Hoops were sold, creating a craze of historical proportions.

The fad originated in Australia. Bamboo rings used for exercise sold there in large numbers in the 1950s. One of the rings was given by an Australian toy company representative to a friend of his, Arthur Melin, co-chairman of Wham-O Manufacturing Co. of San Gabriel, Calif.

It ended up in Wham-O's research and development unit - but nobody there knew what it was supposed to be used for. "It sat around for two or three months," said Wham-O vice president Richard Gillespie. "Nobody knew what to do with it. We rolled it down the street. We put it on pegs."

Then another Australian happened by the company and was questioned about it. Too embarrassed to give a demonstration in front of the people in Wham-O's R & D, he invited Gillespie outside and showed him. So that was it, Gillespie learned. You put it around your waist.

"I took it home to show my wife," Gillespie said. "She said, 'Don't do that. That's obscene.' She thought it was bad. Three months later she was in New York demonstrating it. Shows you how quick the morals change."

Wham-O couldn't supply the 30-inch diameter plastic hoops fast enough. "It proved a natural action for kids to do," Gillespie said. "I think the thing that really kicked it over was its appearance on television.It was featured on a summer replacement for "The Dinah Shore Show.' Sales in New York took off."

"Unfortunately," said company spokesman Goldie Norton, "it happened so fast that 15 or 20 other companies began putting out hoops." As many as 50 million may have been manufactured by other companies in that first six months.

The fad quickly circled the globe in late 1958. In Taipei, about 14,000 persons crowded into a 7,000-seated stadium to watch a demonstration and threatened a riot in the cramped conditions. Three Japanese cities banned hooping in the streets, saying the fad "contributed to an increase in traffic accidents." A Budapest newspaper attacked the craze as "Western idiocy." The city council in Djakrta banned public demonstrations because they "might stimulate passions."

The Washington Post, in an editorial, warned "persons of mature years" of possible physical perils in hooping, concluding: "So our earnest advice is to leave the Hula Hoops to those who know how to make them behave; and these seem to consist exclusively of little girls between the ages of 8 and 10."

But the fad passed as meteorically as it arrived. "Six months after it started, you couldn't give away a Hula Hoop," said Goldie Norton.

"There were warehouses full of Hula Hoops," added Gillespie.

By 1955, the National Ballet Company tried in vain to locate a half dozen in Washington stores to be used in a performance of George Balanchine's "La Sonnambula." Finally, it offered a free ticket to the performance to anyone who could produce a hoop.

In 1967, Wham-O, perceiving "a new generation of kids growing up," as Norton put it, brought back the Hula Hoop, this time with ball bearings inside that made swishing sounds. This was the start of the "Shoop-Shoop Hula Hoop."

"It never has come even close to what it did in 1958," Norton said. But it's become known in the business as "a base product - it's going to make a profit each year. It's been selling steadily the last 10 years."

Gillespie said sales exceed 1 million hoops each year and have risen sharply since the nostalgia craze. The hoops are very much in evidence: Baseball's Los Angeles Dodgers recently used them in spring training; about 1.5 million children in the U.S. took part in Hula Hoop contests last year. This time the hoop could be here to stay.