In landmark rulings for gay rights, the US Supreme Court struck down a law denying federal benefits to homosexual couples and cleared the way for same-sex marriage in California.

Cheers rang out on both coasts among gay marriage supporters after the historic decisions Wednesday, with a large crowd celebrating outside the Supreme Court in Washington and thousands rejoicing in San Francisco and New York.

The nine justices however stopped short of explicitly legalising same-sex marriage nationwide.

In a 5-4 decision, the court first struck down the Defence of Marriage Act (DOMA), which denied federal benefits to married gay and lesbian couples by strictly defining marriage as a union between a man and a woman.

“DOMA is unconstitutional as a deprivation of the equal liberty of persons that is protected by the Fifth Amendment” of the Constitution, read the majority opinion, written by justice Anthony Kennedy.

President Barack Obama, currently traveling in Africa, hailed the decision. “We are a people who declared that we are all created equal — and the love we commit to one another must be equal as well,” he said in a statement.

DOMA denied married gay and lesbians a raft of federal benefits that straight couples take for granted, from tax breaks to family hospital visits and the ability to sponsor a spouse for a residence visa.

The court also said a case on Proposition 8, a 2008 California voter initiative prohibiting same-sex marriage in the nation’s most populous state, was improperly brought before them.

That 5-4 decision enabled the justices to dodge the thorny issue of whether same-sex marriage is a constitutional right, and means that gay marriages will likely resume in California.

Twelve US states plus the district of Columbia now recognise same-sex marriage, but about 30 states have decreed that marriage can only exist between a man and a woman.

“Now we will be married and be equal to every other family in California,” said Kris Perry, a plaintiff in the Proposition 8 case, alongside her partner Sandy Stier on the Supreme Court steps.

“Thank you to the Constitution... But it’s not enough,” added Stier. “It’s got to go nationwide. This can’t wait decades” for marriage equality to be legalised in all 50 states.

Mr Obama is the first serving US President to come out publicly in favour of marriage equality.

White House spokesman Jay Carney said the President had telephoned 84-year-old Edith Windsor, the plaintiff in the DOMA case, and “congratulated her on this victory, which was a long time in the making.”

Obama also called Chad Griffin, head of the Human Rights Campaign, the leading US lesbian, gay, bisexual and transgender civil rights group, and the plaintiffs in the Proposition 8 case to congratulate them on a “tremendous victory.”

Following the DOMA ruling, defence secretary Chuck Hagel said spouses of gays and lesbians in the military would get the same benefits as their heterosexual counterparts “as soon as possible.”

Bill Clinton, who signed DOMA into law when he was President in 1996 but later called for its reversal, applauded the ruling. “Discrimination towards any group holds us all back in our efforts to form a more perfect union,” he said.

US social conservatives however were outraged.

“Today is a tragic day for marriage and our nation,” said the US conference of Catholic Bishops, which urged Americans to pray to God for a review of the Supreme Court’s “wrong” decision.

“Today’s decision is certainly a setback for the traditional values that make up the backbone of our country,” echoed Bob Goodlatte, the Republican chairman of the House of Representatives judiciary committee.

The ruling “has now made the normalisation of polygamy, pedophilia, incest and bestiality inevitable,” added Bryan Fischer, director of issue analysis at the American Family Association.

“Marriage,” said one-time Republican presidential contender Michele Bachmann, “was created by the hand of God. No man, not even a Supreme Court, can undo what a holy God has instituted.”

When asked to react to the statement by Bachmann, an outgoing member of the House of Representatives, Democratic minority leader Nancy Pelosi shrugged. “Who cares?” she told reporters.

Celebrations erupted across the United States after the decisions were announced, including in San Francisco, home to America’s largest gay community and in New York’s Greenwich Village, where hundreds gathered at the famous Stonewall Inn — touted as the cradle of the American gay rights movement — to celebrate.

The petite, elderly Windsor appeared there to thank the crowd for its support.

Windsor was hit with a $363,000 estate tax bill after the 2009 death of her lifelong partner Thea Spyer, whom she had married in Canada. Had the couple been straight, the tax bill would have been much less.

She now can look forward to a refund of that payment, plus a sizeable sum from the government in interest.

Large crowds gathered late Wednesday in San Francisco’s Castro district, the historic gay neighbourhood, where revelers waved US and rainbow flags as they danced in the street.