JAYNE MANSFIELD IS THE ORIGINAL DUMB blonde. Dumb like a fox or Cassius Clay or the hero in "No Time for Sergeants."

She's a "movie star" at a time when they no longer exist. She'd have been right at home back in Hollywood's heyday, when actresses walked diamond-collared leopards on solid silver leashes and lived in 30-room houses.

Jayne lives in a house with 30 rooms or more (she really doesn't know how many rooms there are), a pink-painted mansion with a fountain in the living room, a heart-shaped bathtub, plus a heart-shaped swimming pool in the back yard.

At a time when actors have turned to conservative business suits, live in Switzerland to avoid the tax bite and rise up early in the morning in order to be at the office on time, Jayne is still a fan magazine's delight.

Jayne isn't the girl next door and she doesn't even try to be. She lives, thinks, acts and travels like a movie star. Point a camera in her direction and every muscle in her body leaps to attention.

The blonde bundle, whose measurements sound like something quarterback Bart Starr could bark with authority ("40-22-35!"), arrived in Tokyo complete with a manager and a bearded, beatnik-type described as her "personal secretary." She also. brought three frightened chihuahuas ("Popsicle, Momsicle and Shiksa!").

FOLLOWING A LONG PLANE RIDE AND TWO shows at the New Latin Quarter, the gal with the well-endowed Hope Chest, i.e., the kind of chest most gals hope to wind up with, donned a pair of black leather boots and a black-and-gold miniskirt and set out to find the action.

She squealed with delight when told that Copacabana had an Italian combo on tap every night (her last husband was Italian). And she found it hard to believe when told that the Copa strictly enforces a no-boots-or-miniskirts policy — unless you happen to be Jayne Mansfield.

The minute she was seated (in a dark corner at the management's request), a slightly tipsy American leaned over to roar that he had seen her in "Will Success Spoil Rock Hudson?" (he meant "Hunter").

FLASHING THE FAN A GREAT BIG SMILE, Jayne jumped up to do the frug — or some such dance — while the Italian combo blew loudly in the background. Later, as she sipped on a Coke, she talked enthusiastically about her latest 20th-Fox film, "Tied to a )Married Man."

"Bobby Morse is in it," said Jayne. "And Terry-Thomas. The cast is great. And I play a man ..."

"You play a WHAT?" she was asked.

"Well, I don't actually play a man," admitted Jayne. "But I do dress up in a man's clothing!"

A sigh of relief went up around the table because Jayne Mansfield playing a man would be like trying to pass off the Queen Mary as a tugboat.