The most fashionable women in New York seem to be in a race to have the smallest dog possible. The trendiness is inescapable: Scarlett Johansson, Jessica Simpson, and Britney Spears are rarely seen without their bonsai canines. Star Jones rushed out of a benefit in the Hamptons, saying she simplyhad to get home to her new Maltese. Even $600-a-cut rock-star hairdresser Sally Hershberger, who seems more of a Rhodesian Ridgeback type, is followed at the heels by a mini pinscher named Cherry.

“These girls show me their Birkin bags and say, ‘It has to live in here,’ ’’ says Edward Alava, manager of Le Chien in Trump Plaza, who sold a two-pound Yorkie to Kelly Rowland of Destiny’s Child. Buyers better call ahead. “The teacups are preordered, and they remain with the breeders until they’re sure they will stay small enough. And the smaller, the more expensive.’’

“I’m just waiting for one of those girls to stick a handle on one of them,’’ says Dale Van Pamelan, owner of the New York Dog Spa and Hotel, which counts a one-pound chihuahua among its guests.

It’s not easy being mini. “My clients are even complaining that the smallest fall coats are all gone,” says Dr. Cindy Bressler, who cares for Kate Hudson’s petite Pomeranian. “Some of these dogs can’t fit into the smallest sizes anyway.’’

Vets are having to go to special pharmacies for baby-size pills. “It’s hard to get your hands on the small needles for injections—they’re sold out,’’ says Bressler. Tiny dogs tend to have liver and bone problems, too, she adds, as well as low blood sugar. They are also very needy.

And pity the pooch who grows up. If there’s a poster girl for lilliputian pets, it’s Paris Hilton, who just handed off her teacup chihuahua Tinkerbell to mom Kathy, in favor of an even bittier dog, Bambi. Paris “only likes them when they’re very small, and Tinkerbell got too big,” says someone who knows her. “Tinkerbell is at the larger end of the teacups,” says Dana Miller of Texas Teacups in Garland, Texas, the breeder that sold Tinkerbell to Paris. “Usually, they won’t go over three and a half pounds, but if you fix them or feed them junk …”

The public, though, is still clamoring for some of Tinkerbell’s gene pool. Miller says these dogs normally cost between $2,000 and $3,000. But if they come from Tinkerbell’s bloodline, they’re about $10,000 (and there’s a list). “One woman insisted on this dog from Tinkerbell’s dad, Chester, and her mother Tutu’s sister,” says Shelley Redmon of Texas Teacups. “She paid $13,875. They send us flowers, invitations to restaurants.” New York teacup-seekers include “lawyers, execs from Sony.” And while the breeder isn’t averse to intrafamily mating, it draws the line at incest: “Some breeders mate fathers with daughters to get small dogs, but we would never do that.”

“Teacup is a nice new name” for these pets, notes Van Pamelan. “They used to be calledrunts.”