The US Senate voted down a constitutional ban on same-sex marriage on Wednesday, dismissing arguments by social conservatives that federal intervention is needed to preserve the traditional tie between a man and woman.

The 49 to 48 Senate vote fell short of the 60 votes needed to move ahead with formally considering the amendment backed by US President George W. Bush and mostly Republican lawmakers, let alone the 67 votes required by the Constitution to approve it.

Constitutional amendments must win approval from two-thirds of each house of the US Congress and three-quarters of state legislatures before taking effect.

The US House of Representatives is expected to take up the marriage amendment in July, though Republican leaders do not expect it to pass there either.

President Bush later said in a statement that the Senate vote "marks the start of a new chapter in this important national debate" and that it might take several attempts to build up enough Congressional support to pass the amendment by the necessary two-thirds majority.

"I am disappointed the Senate did not achieve the necessary number of votes to move the amendment process forward," he said.

Democratic critics of the proposed amendment said its Republican authors advanced it to rally socially conservative voters even though lawmakers knew it would be defeated. Opponents of the amendment said that marriage should remain regulated by the states and that the same-sex ban should not be added to the Constitution.

Bush said on Monday that he supports a proposed amendment to the country's Constitution against gay marriage, saying that the amendment "would fully protect marriage from being redefined."

"Marriage is the most fundamental institution of civilization, and it should not be redefined by activist judges," he said in a speech at the Eisenhower Executive Office Building.

State judges have struck down several state gay-marriage bans and court challenges are pending in nine states.

Since 2004, about 8,000 gay couples have married in Massachusetts, the only state to fully recognize same-sex marriages. Six other states and the District of Columbia offer same-sex couples some legal protections.

(Xinhua News Agency June 8, 2006)