With just five months before November legislative elections that are expected to be dominated by issues like the war in Iraq, Mr Bush called for a constitutional amendment defining marriage as solely between a man and a woman.
"I call on the Congress to pass this amendment, send it to the states for ratification so we can take this issue out of the hands of over-reaching judges and put it back where it belongs… in the hands of the American people," he said in a speech to a like-minded audience at the White House.
Mr Bush again targeted what he called "activist judges" who had struck down laws restricting marriage to a union between a man and a woman in the states of Washington, California, Maryland, New York and Nebraska.
"It's an important issue for our country to debate and to resolve. And the best way to resolve this issue is through a constitutional amendment, which I strongly support," said the president.
A constitutional amendment is unlikely because it must garner two-thirds majorities in the Senate and House of Representatives and then win passage from three-fourths of the 50 US states.
But with President Bush's approval ratings at dismal levels, experts say the Republicans need to muster as many of their conservative faithful as possible to prevent heavy losses in the US Congress.