SAN FRANCISCO » For Mina Meyer and Sharon Raphael, two women in their 70s who fell in love more than four decades ago and have been married for more than four years, the U.S. Supreme Court’s pending consideration of a law that prohibits the federal government from recognizing unions like theirs is about more than civil rights. It’s about buying a new roof for their California home, replacing their 2005 Toyota Camry, and ensuring Meyer doesn’t take a financial hit if Raphael dies first.

The Supreme Court will hear oral arguments this month in a challenge to a provision of the Defense of Marriage Act, or DOMA, that denies legally married gay and lesbian couples federal benefits available to heterosexual married couples, including tax and Social Security benefits. A decision is not expected until the end of June, but accountants and tax attorneys anticipating the 18-year-old law’s demise are already encouraging same-sex couples like Raphael and Meyer to seek prospective tax refunds, back retirement payments and other spousal subsidies they may have been denied.

It is unclear how the justices might rule, but the Obama administration and former President Bill Clinton, who signed the act into law, have urged the court to overturn it on grounds that it violates the civil rights of gay Americans. DOMA supporters, including House Republicans led by Speaker John Boehner, argue that Congress — not the court — should decide as public opinion for same-sex marriage grows. Other conservative groups argue that spousal benefits should be reserved only for couples of the opposite sex.

Part of the urgency for couples to act stems from deadlines established under the U.S. tax code, which gives taxpayers three years to file protective claims for income and estate tax refunds. Same-sex couples or surviving spouses who were legally married before or during 2009 would therefore have until April 15 of this year to submit amended returns claiming overpayments on income for that tax year, said Vickie Henry, a senior staff attorney at Gay & Lesbian Advocates & Defenders.

At the time, gay unions were legal in Massachusetts, Connecticut, Iowa and Vermont, and briefly had been in California. New York and the District of Columbia, which have since legalized same-sex unions, also recognized marriages performed in other states or countries.

While married couples from those jurisdictions would have the strongest cases, couples from states such as Hawaii, Nevada and Illinois that treat domestic partnerships and civil unions as the same as marriage for tax purposes might also see federal refunds depending on how the Supreme Court rules, said Pat Cain, a federal tax expert at the Santa Clara University School of Law.

“On the income tax side, anybody who would benefit from filing jointly and who would be eligible to do so if DOMA falls should consider filing amended tax returns for the applicable years,” Cain said.

The sums at stake are not inconsequential. The case the justices accepted, for example, involves a New York state widow, Edith Windsor, 83, who is seeking a refund of the $363,000 she had to pay in estate taxes after her wife, Thea Spyer, died in 2009. If Windsor had not been married to another woman, her tax bill would have been $0 because married U.S. citizens are allowed to pass their assets onto their spouses tax-free — but only if the surviving spouse is of the opposite sex.

Gerald McIntyre, directing attorney at the National Senior Citizens Law Center, said Social Security benefits, which kick in based on the date of application, are where gay couples have lost the most and stand the most to gain.

Lower-earning spouses such as Meyer have been doubly penalized under DOMA, McIntrye said, first by being unable to claim the spousal benefit that allows married heterosexuals to increase their monthly benefits by drawing half of a husband or wife’s Social Security, then being deemed ineligible for survivor benefits that are equal to what a deceased spouse got in retirement each month.

A 2009 study by The Williams Institute, a think tank on sexual orientation and the law at the University of California, Los Angeles, estimated that gay couples received an average of $3,060 less a year in Social Security benefits than married straight couples. For lesbian couples, the disparity rose to $5,412. The same study found that gay or lesbian widows or widowers lost out on more than $5,700 a year in survivor benefits than their straight counterparts received.

In the case of retirees Raphael and Meyer, it could mean an additional $7,335 year in Social Security benefits because Meyer, who worked in office jobs and a bookstore, would be entitled to the Social Security benefits of Raphael, who earned considerably more as a college professor for 40 years. That would boost their fixed monthly income by about 10 percent. Last year, on the advice of a professional colleague and with the high court poised to decide if DOMA is constitutional, Meyer applied for more than a year’s worth of retroactive benefits as well as bigger future checks if the law is struck down.

“This is not the only money we live on, but it does make a big difference,” said Meyer, 73, who also would see her Social Security checks more than quadruple in the event she is widowed and the court overturns the act. “That $700 a month is $700 a month.”

Other married same-sex couples may end up paying more in taxes if DOMA is overturned, due to the so-called federal “marriage penalty.” Janis Cowhey McDonagh, a tax attorney in the New York office of accounting firm Marcum LLP, (equals) has been encouraging many of her clients in same-sex marriages to get their returns in order before the Supreme Court rules.

“If it’s better for them to file single even though they are married, I tell them they need to file before DOMA comes down, because if DOMA comes down, they won’t have the choice,” she said.