Americans insure everything from precious jewels to contact lenses, so J. Scott Henderson figured that, offered the right deal, they'd insure their pets.

Henderson founded the Animal Health Insurance Agency Inc. in 1983. The company is now writing $1.5 million worth of health insurance policies annually on 20,000 dogs and cats in 49 states."When my investors and I started this, people would say, 'Insurance is going to the dogs.'" he said. "They don't laugh any more."

Pet health insurance has been common in Europe for half a century. But the idea has been slow to catch on in the health-conscious United States, where 30 such companies have failed since 1945, the American Veterinary Medical Association says.

Experts say Henderson's and the four or five other companies now offering pet health insurance in the United States entered the market at the right time, as attitudes toward pets were changing and increasingly sophisticated medical treatments became more common.

"It's going to be successful this time," said Sam Strahm, a veterinarian in Pawhuska, Okla., and president-elect of the AVMA. "There are individuals where their pet is certainly part of the family, and they are going to become more comfortable using third-party payments."

Henderson's major competitor is the Veterinary Pet Insurance Co. in Santa Ana, Calif., which was started in 1982 and wrote about 60,000 new policies last year, said its medical director, Dr. James R. Connoyer.

VPI is licensed to offer policies in 37 states through its underwriter, the Scottsdale, Ariz.-based National Casualty Co., Connoyer said.

There are more than 100 million dogs and cats in about 60 million U.S. households, AVMA figures show. Americans spend $13 billion a year on pets, on everything from gourmet pet food, beef-flavored tooth paste and pet clothes to increasingly sophisticated pet health care, including CAT scans, chemotherapy and heart pacemakers.

In 1987 cat owners spent $63.83 per household on veterinary care, 43 percent more than the 1983 average of $44.59. Dog owners' veterinary expenditures rose 16 percent in the same period, from $74.51 per household to $86.73.

For $36 a year, Henderson's policy holders can insure their pets against catastrophic illness and accidents, with a $250 deductible per claim. For $89 a year, the deductible drops to $40. Not covered are routine procedures such as inoculations and spaying.

The policies are underwritten by Combined International Corp. in Chicago, which currently caries assets of more than $5 billion.

Henderson's goal is to insure 1 percent of household pets within five years. Sales have increased between $300,000 and $400,000 a year since the company started offering policies nationally in 1985, he said.

Among Henderson's customers is a wealthy Newport, R.I., woman who has policies on her 22 dogs.

Robert Goldstone of Oceanside, N.Y., took out a policy for his 9-year-old Yorkshire terrier, Tarzan, about 1 1/2 years ago.

"A dog gets sick just like a human," he said. "I'm sorry I didn't have it years ago.

It was the death of his black Labrador retriever, Bo, a decade ago that stirred Henderson's interest in pet health insurance. The 9-year-old dog was stricken with bone cancer in 1979, when Henderson was going through the turmoil of a divorce. Rather than spend $2,000 for treatment, he had Bo put to sleep.

A few months later, Henderson was at a cocktail party where he met Brian Sutton, president of the Equine & Livestock Insurance Co. in England.

"The whole thing intrigued me," Henderson said. "I felt there was a lot of folks out there who probably felt as strongly or more so than myself and here we are in the U.S. of A. and we have insurance that insures contact lenses, we have insurance that does the whole thing, and pets to me made sense."

Henderson and two other investors started out in Mount Vernon, N.Y., and sold 3,000 policies in New York state during the first two years. That gave them the statistical information they needed to set rates and establish a track record as a legitimate company, he said.

The company has so far marketed its plan primarily through veterinarians, who are urged to carry brochures in waiting rooms. But there's one problem with that approach: "You get a lot of sick pets," Henderson said.

So this year the company is talking to a direct-mail outfit in California and advertising on several cable television networks, including the Christian Broadcasting Network.

"I would be less than frank with you if I said, "I'm doing it just because I love pets," Henderson said. "I'm doing this too because I think there is a need and...I can see if we do it right, we as a company can make some money."