PORTLAND (AP) – Anthem Blue Cross Blue Shield of Maine is proposing an average rate increase of 13.6 percent for about 39,000 Medicare Companion policyholders.

The plans, which last increased 3.4 percent in 2004, cover gaps in the federal health insurance program for senior citizens and most recently increased in cost by 3.4 percent last year.

Rate increases averaging 15.5 percent are also proposed for another 35,000 people enrolled in the HealthChoice program.

Rate increases are subject to approval by the state insurance superintendent, who will take public testimony on the Medicare Companion proposal on Oct. 17 and HealthChoice on Nov. 9.

The state attorney general’s office plans to intervene on behalf of policyholders, Assistant Attorney General Christina Moylan said Thursday.

“Both requests are substantial, so they warrant scrutiny in our view,” Moylan said. “We’re getting more information from the company and figuring out if we think there is fat and where it is.”

Anthem is dominant in Maine’s individual insurance market in Maine, with 89 percent of business, according to the Bureau of Insurance.

Increasing rates for next year “is not something we do lightly or with any enthusiasm given the past increases,” said Anthem spokesman Mark Ishkanian. “But the numbers and the experience show what we need to do to have the money next year to pay claims for those members.”

Ishkanian suggested a rate increase for HealthChoice members could exceed what Anthem has proposed if the state assesses a fee known as a savings offset payment on insurance companies and large self-insured employers to help finance the state-subsidized DirigoChoice health insurance program.

A plan for determining the fee has been filed with the insurance superintendent, and a decision is expected next month.