President George W. Bush, facing ever-sagging public opinion polls, will return to right-wing extremism to try and revive his fortunes, promoting a constitutional ban on gay marriage on the eve of a Senate vote next week.

Though the proposed constitutional amendment against same-sex marriage stands little chance of passing, it is one of several hot-button causes Republicans are championing to appeal to right-wing voters ahead of November’s congressional ballot.

Bush planned to use his weekly radio address on Saturday and a White House speech on Monday to push for the amendment that would allow states to recognize only marriages between men and women, administration officials said on Friday.

Bush has never made a secret of his views on the issue but has rarely talked about it in public until now.

“He believes the institution of marriage is between a man and a woman,” White House spokesman Tony Snow told reporters. “The president’s made it clear what he wants. He would like to see the Senate pass the bill.”

The Senate Judiciary Committee approved the amendment along party lines after a heated session on May 18. Because the measure seeks to change the Constitution, it must pass both houses of Congress by a two-thirds majority and then be approved by at least 38 states.

The full Senate will take up the measure on Monday with a vote expected later in the week, but the bill’s sponsor, Colorado Republican Wayne Allard, has acknowledged he has far fewer than the 67 votes needed to win passage.

Bush is raising his profile on the issue at a time when his public approval rating stands at around 30 percent, the low point of his presidency.

Bush used to be able to count on overwhelming support from fellow Republicans and conservatives.

But the Iraq war and a series of political blunders have chipped away at that backing, leaving many Republicans worried about losing control of Congress to the Democrats in November.

Critics say the Republicans are trying to exploit anti-gay prejudice to galvanize their conservative base.

Defending Bush’s decision to speak out, Snow denied the president was acting out of “political expedience” and insisted he was taking up the issue because it was “politically ripe.”

A similar effort failed in the Senate in 2004. Gay marriage has been a hot topic since a Massachusetts court ruled in 2003 that the state legislature could not ban it, paving the way for America’s first same-sex marriages in May the following year.

At least 13 states have passed amendments banning gay marriage while two — Vermont and Connecticut — have legalized civil unions.

Just over half of all Americans oppose same-sex marriage, according to a March poll by the Pew Research center, down from 63 percent in February 2004.