Gay couples who wed would gain access to roughly 300 benefits and protections now afforded married couples in Maine if the state's new same-sex marriage law takes effect, gay-rights supporters said Thursday.

Those benefits include easier access to health insurance, and child custody and survivor rights after a spouse's death.

But gay couples still would not have hundreds of protections codified in federal law, supporters of gay marriage say, and in many cases would continue to pay financial penalties based on their sexual orientation.

"We will gain many of the benefits but not the equality of marriage," said Mary Bonauto, a lawyer at Gay & Lesbian Advocates & Defenders, a Boston-based group that was active in pressing for passage of the Maine law.

Bonauto, a Portland resident, is the lead attorney in a lawsuit filed in federal district court in Boston that challenges the denial of key legal protections to same-sex couples relating to Social Security, income tax and other marriage-related benefits.

Her group's goal is to take the issue to the U.S. Supreme Court, unless Congress modifies the 1996 Defense of Marriage Act, which limits 1,138 benefits and protections to marriages between a man and a woman.

On Thursday, House Speaker Nancy Pelosi said same-sex marriage isn't a priority in Congress. She cited the economy, energy policy and health care as overarching concerns.

On Tuesday, the City Council in Washington, D.C., voted to recognize same-sex marriages from states that approve them. Congress has final say over laws passed in the nation's capital and has 30 days to review it.

On Wednesday, Maine became the fifth state to allow gays to wed, and New Hampshire's legislature sent a gay-marriage bill to the governor the same day.

Meanwhile, Maine election officials say opponents have filed a formal challenge to the same-sex marriage law. In order to force a people's veto referendum, they must collect petition signatures amounting to at least 10 percent of those who voted in the last gubernatorial election.

The state has been unable to estimate the overall financial impact of the new law. A preliminary statement filed with the bill in the Legislature cited possible increases and reductions in fees and real estate taxes, but no dollar figure.

If a repeal effort fails in Maine, gay-rights advocates say, state benefits could extend to at least 5,000 Mainers who identified themselves on the 2000 census as domestic partners, if they choose to marry. But the census survey is nearly a decade old, and some gay couples are reluctant to highlight their sexual orientation, said Betsy Smith, executive director of Equality Maine, a key supporter of the new law.

It's unclear how many gay couples would marry and qualify today for the benefits of marriage in Maine, she said, but the benefits can add up to thousands of dollars a year for a family in insurance and tax treatment.

"When you fall in love with someone and want to get married, you never think of all the protections," Smith said. "You just take them for granted."

For example: A typical group health insurance plan covering a family and offered by Anthem Blue Cross and Blue Shield costs roughly $17,000. Under current Maine law, a gay worker could extend health benefits to a partner and children, but has to sign an affidavit that the couple have lived together for at least six months and are responsible for each other's common welfare.

The new law would drop that requirement – but with a catch. Federal law says the worker must treat those health benefits as taxable income, at the fair market value of the insurance.

That seems unfair to Carolyn Thomas of Falmouth, who works and covers her partner and daughter on her employer's health plan. The penalty extends to the contribution her employer makes to the plan.

"I'm taxed on the excess contribution that my employer...