As analysts predicted, the court took up one challenge to the 1996 Defense of Marriage Act (DOMA), which defines marriage as the legal union of one man and one woman and denies federal benefits to married same-sex couples.

Benefits enjoyed by heterosexual married couples but denied to gays include inheritance rights, tax breaks, filing of joint income tax returns, and health insurance coverage.

President Barack Obama’s government does not support this view of marriage and would like the law to be overturned, but conservative campaigners are urging the Supreme Court to rule that the act is constitutional.

The specific case to be heard involves Edith Windsor, a lesbian legally married in Canada who has been told to pay tax on inheriting the estate of her deceased partner.

The Supreme Court will rule whether DOMA violates the guarantee of equal protection under the law as guaranteed by the fifth amendment of the US constitution.

It will also decide if the Obama administration’s position that DOMA is unconstitutional deprives the Supreme Court of jurisdiction, and whether a complaint by some US lawmakers has legal standing.

Justice Elena Kagan, as Obama’s former solicitor general has recused herself on some of the cases in which she had played a role, but this is one on which she can participate.

Kagan’s participation avoids the potential for a 4-4 split on the nine-member bench.

The other case taken up was brought by supporters of “Prop 8,” a referendum that passed in California in 2008 that defined marriage as being between a “man and a woman” -- but which was overturned by a court of appeal.

If the Supreme Court throws out their appeal, California -- the country’s most populous state -- will in effect become the 10th state to permit gay marriage.

In Hollingsworth v Perry, the court will decide whether the 14th amendment of the US constitution, which requires states to provide equal protection under the law to all people, prohibits California from banning gay marriage.

The Supreme Court will also decide whether the petitioners have legal standing in the case.

“Today is a milestone day for equal justice under the law and for millions of loving couples who want to make a lifelong commitment through marriage,” said Chad Griffin, president of the Human Rights Campaign, a national gay rights organisation.

“As the court has ruled 14 times in the past, marriage is a fundamental right and I believe they will side with liberty, freedom and equality, moving us toward a more perfect union as they have done in the past.”

The conservative Family Research Council was also pleased, with president Tony Perkins saying in a statement: “Virtually nothing is more important to the future of our country than marriage and the family.”

“The argument that the authors of our Constitution created or even implied a ‘right’ to redefine ‘marriage’ lies outside our constitutional law,” Perkins added.

Justices did not say what they planned to do with eight other gay marriage petitions they debated behind closed doors on Friday.

It is likely that these, along with a last-minute case on the gay marriage ban in Nevada, will not be heard. But the Supreme Court could also rule that whatever decision it reaches in June should prevail over all the pending cases -- not just the ones heard.

As a country, the United States appears to be slowly moving towards tolerating same-sex unions.

An opinion poll by USA Today/Gallup released this week ahead of the court’s decision showed that 53 per cent of Americans believe same-sex marriage should be legal, up from 40 per cent just three years ago.

Within the lesbian, gay, bisexual or transgender (LGBT) community, the poll showed that 91 per cent felt residents in their communities had become more accepting of homosexuals in recent years.

Among those whose position has evolved over this period is Obama himself, who always backed strong protections for gay and lesbian couples, but only came out openly in favour of homosexual marriage earlier this year.

“I’ve just concluded, for me, personally, it is important for me to go ahead and affirm that I think same-sex couples should be able to get married,” Obama said in a May interview with ABC News.

The president said however that a decision on whether to legalize gay marriage should be left to individual states.