The Montgomery County Council is considering a plan that would make available unique low-cost health insurance to all persons living or working in the county to pay for medical bills that run over $100,000.

The voluntary plan is intended to supplement regular health insurance coverage, which often stops at $50,000 to $100,000, said council Vice President William E. Hanna Jr., sponsor of the bill. Because the pool of insured persons could be so large, premiums for the policy could be offered at a minimum cost of $25 to $50, he added.

Annual premiums for similar private insurance ranges from $50 to $150, he said.

"With advances in medical technology and the escalation of health care costs . . . all but the wealthiest of families can be bankrupted by family illnesses," Hanna said.

Yet insurance industry spokesmen questioned the demand for such a plan, saying most people already have regular private policies or policies through their employers with payment limits higher than $100,000.

"Most plans that have comprehensive and major medical programs have a $1 million maximum. And the average resident of Montgomery County has better coverage than most residents in the country," said Bill Von Bargen, general manager of the employe benefits division of Aetna Life & Casualty.

The industry representatives said few medical bills come to more than $100,000. Amy Biderman of the Health Insurance Association of America said a 1976 study by the industry trade group of 7.6 million health insurance claims found that only nine in 1 million claims that year reached $100,000.

Insurance experts also questioned the financial protection that the plan would provide. "I don't think it will help people who don't have health insurance because they'll be broke before it helps them," said Robert Hunter, president of the National Insurance Consumer Organization. "Who can afford $100,000?"

Hanna said he has no specific figures on how many county residents need the extra insurance, but the Health Insurance Association of America estimates that 15 percent of the national population have no health insurance.

Pamela Farley of the National Center for Health Services Research of the U.S. Public Health Service, said that an even larger group, about 26 percent of the nation's population, have no insurance, only sporadic insurance or inadequate insurance. In an area such as Montgomery County that has an above-average income level, she said, about 14 percent of the residents would need the service.

State assistant insurance commissioner Thomas Raimondi praised the Montgomery County legislation introduced Tuesday and said it fills a gap in medical insurance coverage today.

"There's a need for some kind of coverage like this. I think it's very responsible for Montgomery County to address this," Raimondi said.

The county would act only as the administrator of the program after selecting an insurance company to offer the policy, Hanna said. There is no estimate of the administration costs, he added.