BOSTON — State law in Massachusetts bans municipalities from passing breed-based dog ordinances and now lawmakers are hearing a push to ban insurers from refusing to issue a policy, canceling a policy or charging an increased premium based upon a homeowner's ownership of any specific breed of dog.

Framingham Rep. Jack Lewis told the Financial Services Committee Tuesday that dogs can be viewed very differently by insurers versus, for instance, the American Kennel Club. Certain breeds, he said, have received "bad raps" that are not based on their behavior.

"The current law is based on false understanding of dog breeds," Lewis said.

But dog bites are the "single biggest cause of loss for us," causing physical and financial harm that "is tremendous," said Frank O'Brien, testifying for the Property and Casualty Insurers Association of America, whose members write about half of the homeowner's insurance policies in Massachusetts.

"There is no single bigger risk to the insurance industry than the presence of a dog," said O'Brien, who said he's a former dog owner (Molly) and his family is prodding him to become one again. The insurance group opposes the bill.

Testifying for the bill, members of a Massachusetts Society of Prevention of Cruelty to Animals (MSPCA) panel told lawmakers that dog owners who do not disclose their ownership may face financial liabilities, while those who do may be unfairly charged based on breed lists.

More lawmakers are signing on as supporters of the bill (H 544/S 533), said Kara Holmquist of the MSPCA, who said insurance-related questions are the top issue among callers to her organization. "We're seeing increased interest in this issue," she said.

Dog owners must be responsible for the training and behavior of their dogs, but dogs should for insurance purposes be judged based on their behavior rather than what they look like, said Jennifer Clark, testifying on behalf of the American Kennel Club, which promotes responsible dog ownership.

Rep. Chris Walsh of Framingham said breed is not the only factor in assessing whether dogs are dangerous. "So much of what a dog is is a relationship with an owner and a family," Walsh said.

Supporters of the bill also said the existing situation, and growing lists of breeds maintained by insurers, is forcing homeowners to give up their pets, putting additional burdens on animal welfare agencies.

Under the bill, if any individual dog has been designated as a dangerous dog under current law, the legislation would not prohibit an insurer from refusing to issue or renew or from canceling any such contact or policy, nor from imposing an increased premium or rate for such a policy or contract.

O'Brien said insurers write policies based on dog bite data and claims experiences. Some insurers refuse to cover certain dogs, he said, while others will visit a property and see firsthand if a dog has dangerous tendencies before deciding whether to cover the pet.

"When it comes to risks of all types we predicate our risk analysis based upon large amounts of data that predict whether or not an event is going to take place," O'Brien said. "We price acordingly."

He added, "Any dog can bite. Any dog can cause an insurance claim and sometimes those claims can be pretty significant, pretty horrific."

During a break from the hearing, O'Brien said there's no single industry-wide list of breeds of concern to insurers and called dog bites an "epidemic." He said insurers have detected an increase in the number of dogs "known for their aggressiveness."

Asked to speculate how prevalent it is for homeowners to fail to disclose dog ownership to insurers, O'Brien said insurers rely on homeowners disclosing features of their home in their insurance applications, including dog ownership or the existence on their property of a swimming pool, trampoline, or a wood stove.