Image caption Analysts expect the justices will hear challenges to the Defense of Marriage Act

The nine justices of the US Supreme Court have put off until next week a decision on whether to consider the constitutionality of same-sex marriage.

They discussed cases to be heard in the coming year, including a challenge to the federal Defense of Marriage Act (Doma).

The 1996 law states that marriage can only be between a man and a woman.

The high court would hear any cases chosen by the coming spring and make a ruling by the end of June 2013.

Thirty-one of the 50 US states have passed constitutional amendments banning gay marriage, while Washington DC and nine states have legalised it, three of them in the recent US elections.

All of the possible cases before the Supreme Court deal with three laws:

Doma, which prevents legally married gay couples from receiving federal marital benefits

Proposition 8, an amendment to California's state constitution that overturned an earlier law legalising gay marriage

Part of a 2009 Arizona law granting marital benefits only to legally married state employees (gay marriage is not legal in Arizona).

Each of the laws has been struck down in rulings by lower courts.

The biggest question before the court is whether the right to marry must be extended to same-sex couples because it is a fundamental right under the US constitution's guarantee of equal protection to all citizens.

Analysts expect the Supreme Court will agree to hear challenges to Doma.

The federal law, signed by former President Bill Clinton, has been overturned by four federal courts and two courts of appeal, which said Doma unfairly discriminated against same-sex couples.

President Barack Obama, who backed gay marriage in May, also took the unusual step of announcing that his administration would not back Doma in court.

But the law is supported by Republicans in Congress.

A CBS News poll on Friday found that 51% of Americans thought gay marriage should be legal, while four in 10 did not.