Anger over rising health care costs swelled again Thursday as doctors, insurers and politicians debated whether the state is adequately regulating insurance rate hikes.

With premiums for individual health plans increasing an average of 20.7 percent this year in Connecticut, Attorney General Richard Blumenthal and state Healthcare Advocate Kevin Lembo want to overhaul the state system to make rate hikes "reasonable." The current regulation is based on actuarial science and insurer-provided information, and says rates must be "not excessive."

"This 'reasonable' test will be nearly impossible to apply and likely to lead to inconsistent results," said state Insurance Commissioner Thomas Sullivan.

Sullivan and insurers say premiums merely reflect rising medical costs — prescription drugs, new medical machinery, doctor fees. Additionally, insurers say utilization is excessive because doctors are ordering tests to defend themselves against lawsuits, and doctors are trying to make more profit from patients with private insurance to balance a loss on services provided to patients with public health plans.

Doctors say their pay has been static or even declined.

"By hook or crook, they're always trying to pay physicians less by denying care, denying and reducing payments for services already provided, increasing red tape and causing patients to pay more of their health care costs," said Matthew Katz, executive vice president of the Connecticut State Medical Society.

Lembo and Blumenthal argued that rate hikes should be regulated by another metric — the public's ability to pay.

"Why is it that people, individuals and businesses have accepted increases in their insurance premiums? It's because they've had no power to change the outcome, no voice in the process. That all changes today," Lembo said Thursday, before a legislative hearing on the issue.

A bill proposed by Lembo and Blumenthal would require public hearings for all rate hikes to individual health plans — not group plans sold through employers. Current law gives the state insurance commissioner the right to hold a public hearing if he deems necessary.

The bill would also require insurance companies to disclose the supporting documentation for medical expenses that drive up premiums. Current law deems much of that information proprietary, although the state Insurance Department has access to it.

Rate increases in 2010 for group plans have averaged 12 to 19 percent, according to a legislative report.