AUGUSTA — Gov. Paul LePage capped his administration’s biggest political victory to date Tuesday, signing a health insurance reform bill that’s designed to lower costs and cover more Mainers through a series of market changes.

“It was a tough-fought battle,” he said. “I’m proud of the Republican leadership for staying there and working this through.”

The Republican governor signed the bill into law at a table set up in the State House Hall of Flags, with about 75 Republican lawmakers standing behind him.

House Speaker Robert Nutting, R-Oakland, said the bill will lower the cost of health insurance, something Republicans have been trying to do for many years. He praised legislators for standing up to “scare tactics” and “special interests.”

“This is a great day for the state of Maine,” Nutting said.

Meanwhile, the Maine Democratic Party sent out a news release that called the new law “one of the most stunning broken promises in Maine political history.”

Democrats in the Legislature have complained that they had no role in drafting the legislation, which overhauls the health insurance market for about 40,000 people — those who buy independently or through employers whose companies have 50 or fewer workers.

It affects almost every policyholder in the state because it adds a tax on premiums of as much as $4 per person per month, to help cover people with high medical costs.

Democrats said Republicans have opposed any kind of tax increase for years, and are now imposing a $24 million tax after only five months with majorities in the Legislature and a Republican governor.

Ben Grant, the Maine Democratic Party’s chairman, said Republicans have supported requiring a two-thirds vote by the Legislature and a statewide referendum to raise any tax.

“Can Maine people afford to trust anything Governor LePage and the Maine GOP say ever again?” he asked.

In an interview after he signed the bill, LePage said the $4 monthly assessment is a small amount of money relative to the considerable savings that many Maine families will enjoy. He said a family of four now pays $1,400 a month for health insurance, and the bill will lower the cost by 30 percent to 40 percent.

“My recommendation is: Let’s see it take effect and see if the cost goes up,” he said.

The Maine People’s Alliance said it is considering a people’s veto referendum campaign to stop the law from taking effect. Calling the law a “handout to the insurance companies,” the alliance also expressed worries about its effect on older and rural Mainers.

The law gives insurance companies more leeway in how much they can charge policyholders based on age.

Starting July 1, 2012, some people could pay three times as much for their policies as other people, because of their age. By 2014, the ratio will be 5 to 1. Current law limits the ratio to 1.5 to 1. In 2014, the federal Affordable Care Act will set the ratio at 3 to 1.

While Nutting, the House speaker, said the law is based on proven systems in dozens of other states, Senate Minority Leader Barry Hobbins, D-Saco, said it was rushed through without a comprehensive actuarial analysis by the state Bureau of Insurance.

– Glenn Adams of The Associated Press contributed to this report.

MaineToday Media State House Writer Tom Bell can be contacted at 699-6261 or at: tbell@mainetoday.com