Sacramento, Calif. ? A bill that would require most dogs and cats in California to be spayed or neutered has brought howls of protest from breeders and threats from the American Kennel Club to pull the nation’s second-largest dog show from the state.

Breeder Janet Wahl grooms Pipper, a 2-year-old Havanese, at her Newcastle, Calif., home. Many breeders, including Wahl, are against a proposed bill that would require most dogs and cats in California to be spayed or neutered.

The measure – which would be the most sweeping statewide pet-sterilization law in the country – passed the Assembly by a single vote earlier this month and goes next to the Senate, where its prospects are uncertain despite the support of animal-loving celebrities such as Pamela Anderson, Lionel Richie and retired “Price Is Right” host Bob Barker.

It is aimed at reducing the estimated 500,000 unwanted dogs and cats that are destroyed in California animal shelters each year.

“The more animals neutered and spayed, the fewer animals born, the fewer animals coming into our shelters, and fewer animals are euthanized,” said Pat Claerbout, president of the California Animal Control Directors Association.

The bill – sponsored by Assemblyman Lloyd Levine, a Democrat from Southern California who is also pushing to phase out the incandescent light bulb – would require pet owners to sterilize their dogs and cats by the time they are 4 months old, or face a $500 fine.

Licensed breeders of purebreds would be exempt. But the law does not spell out which dog and cat breeds would be covered, and breeders wanting an exemption would have to apply for one from their local animal control authorities. The bill leaves it up to counties and cities to set the price.

Professional breeders complain that the measure would do little to curb “backyard breeders,” that it would drive up their costs and entangle them in bureaucracy, and that it would amount to social engineering for animals.

“I think what’s happening in California is socialism in its prime,” said Janet Wahl, who lives near Sacramento and breeds Havanese and Yorkshire terriers. She said she fears the government will put itself in the position of deciding which dog breeds can reproduce and which cannot.

In the Sierra foothills, officials in rural Amador County complained it would be costly and burdensome for local governments to enforce the measure. And worse, they said, it could lead to the demise of the beloved mutt.

The American Kennel Club, which every December sponsors the Eukanuba National Championship in Long Beach, the nation’s largest dog show after New York’s Westminster Kennel Club event, has threatened to pull the internationally televised competition out of California if the bill succeeds.

Last year’s show drew 28,000 people and was credited with injecting $21.7 million into the local economy.

Its 5,000 member clubs have organized a national letter-writing campaign, while the 122-year-old organization has formed its first ever political action committee to fight what it calls “anti-dog laws” in California and elsewhere.