The Senate on Wednesday rejected a constitutional amendment to ban gay marriage, but supporters said new votes for the measure represent progress that gives conservative Republicans reason to vote on Election Day.

The 49-48 vote fell 11 short of the 60 required to send the matter for an up-or-down tally by the full Senate. The amendment's failure was no surprise, but supporters said the vote reflected growing support among senators and Americans.

"We're building votes," said Sen. David Vitter, R-La., who is among supporters of the ban who were not in the Senate when the amendment was last voted on in 2004. "That's often what's required over several years to get there, particularly to a two-thirds vote."

A majority of Americans define marriage as a union of a man and a woman, as the proposed amendment does, according to a poll out this week by ABC News. But an equal majority opposes amending the Constitution on this issue, the poll found.

"Most Americans are not yet convinced that their elected representatives or the judiciary are likely to expand decisively the definition of marriage to include same-sex couples," said Sen. John McCain R-Ariz., a possible presidential candidate in 2008. He told the Senate on Tuesday he does not support the amendment.

The measure's defeat in the Senate is by no means its last stand, said its supporters.

"I do not believe the sponsors are going to fall back and cry about it," said Sen. Orrin Hatch R-Utah. "I think they are going to keep bringing it up."

The House plans a redux next month, said Majority Leader John Boehner, R-Ohio.

"This is an issue that is of significant importance to many Americans," Boehner told reporters. "We have significant numbers of our members who want a vote on this, so we are going to have a vote."

The defeat came despite daily appeals for passage by President Bush, whose standing is troubled by sagging poll numbers and a dissatisfied conservative base.

The Vatican also added muscle to the argument Tuesday, naming gay marriage as one of the factors threatening the traditional family as never before.

Democrats, all of whom except Sen. Ben Nelson of Nebraska oppose the amendment, said the debate was a divisive political ploy.

"The Republican leadership is asking us to spend time writing bigotry into the Constitution," said Sen. Edward Kennedy of Massachusetts, which legalized gay marriage in 2003. "A vote for it is a vote against civil unions, against domestic partnership, against all other efforts for states to treat gays and lesbians fairly under the law."

In response, Hatch fumed: "Does he really want to suggest that over half of the United States Senate is a crew of bigots?"

Forty-five of the 50 states have acted to define traditional marriage in ways that would ban same-sex marriage ¡ª 19 with constitutional amendments and 26 with statutes.

The amendment would prohibit states from recognizing same-sex marriages. To become law, it would need two-thirds support in the Senate and House, and then would have to be ratified by at least 38 state legislatures.

The Senate tally Wednesday put the ban 18 votes short of the 67 required for approval of a constitutional amendment.