US President George W Bush has used his weekly radio address to voice support for a constitutional amendment which would ban gay marriage, ahead of a Senate vote on the issue.

The amendment, which would prohibit states from recognising same-sex marriages, needs a two-thirds majority in the Senate and House, and then would need to be ratified by at least 38 state legislatures before becoming a law.

Mr Bush told the nation, “Ages of experience have taught us that the commitment of a husband and a wife to love and to serve one another promotes the welfare of children and the stability of society.

“An amendment to the constitution is necessary because activist courts have left our nation with no other choice.”

So far, a positive vote looks highly unlikely, according to the Seattle Post-Intelligencer, which reports that supporters of the amendment are struggling to find even half of the 100-member Senate to back it, let alone the two-thirds needed.

Several Republicans oppose the measure, and so far only one Democrat Senator Ben Nelson says he will vote for it.

Republicans even closer to the Bush camp have indicated they will not support the amendment. Vice President Dick Cheney, whose daughter Mary is a lesbian, has vocally opposed the measure.

The Senate Judiciary Committee narrowly approved the amendment on May 18 2006 in a vote along party lines that had Democrats and Republicans in a shouting patch.

The Massachusetts Supreme Court decided to legalise such marriages in 2003. A year later, San Francisco Mayor Gavin Newsom issued thousands of marriage licenses to gay couples, which have since been revoked.

Initiatives banning same-sex marriages are expected to be on the ballot in Idaho, South Carolina, South Dakota, Tennessee, Virginia and Wisconsin this November. In 2004, 13 states approved initiatives prohibiting gay marriage or civil unions.

“The president firmly believes that marriage is an enduring and sacred institution between men and women and has supported measures to protect the sanctity of marriage,” White House spokesman Ken Lisaius said.

The Senate will vote on the issue tomorrow.