WASHINGTON (CNN) -- The Senate rejected Wednesday a bid to amend the Constitution to essentially ban same-sex marriage.
Republicans pushed the plan even though supporters conceded the measure did not have enough votes to pass.
Proponents failed to get the 60 votes needed to end debate and move to a vote on the actual amendment. The Senate vote was 49-48 to end debate.
Opponents called the measure an election-year ploy that wasted precious time on the legislative calendar.
"This is not about the preservation of marriage. This is about the preservation of a majority," Sen. Richard Durbin, D-Illinois, said as debate started Wednesday. "I think, sadly, most people realize there's political motivation here."
Republican senators said 45 states have passed laws or constitutional amendments defining marriage as a pact between a man and a woman. "The voice of the people has been heard loud and clear," Sen. Wayne Allard, R-Colorado, said.
The real impetus behind the debate was to energize conservative voters this fall, CNN's Dana Bash reported.
Those conservatives feel like Republicans they've sent to Washington "have sort of turned their backs on them on key issues that they care about like same-sex marriage... That is why you're seeing the Senate take up those issues this week," Bash said.
Sen. Ted Kennedy, a Massachusetts Democrat, denounced the proposed amendment Tuesday as "an instrument of bigotry and prejudice," which he said was designed by the GOP leadership "to try to bring Republican senators out of the ditch of disapproval."
And Senate Minority Leader Harry Reid, a Nevada Democrat, said that "the reason the Senate Republicans are pushing this marriage amendment is because they don't want to address the real issues of this country."
"This is an effort by the president and the majority in the House and the Senate to distort, to misdirect what the real issues are," he said.
The vote began around 10 a.m., after a final hour of debate. The Senate began debate on the amendment Monday afternoon.
Even if the measure had been able to clear the procedural vote, a two-thirds majority -- 67 votes -- would be required for final approval of a constitutional amendment -- an even higher hurdle to overcome.
The last time the Senate voted on the amendment, in July 2004, only 48 senators supported it and 50 were opposed. Spurred on by religious conservatives in his political base, President Bush had called on the Senate to approve the amendment, saying it was necessary to protect the institution of marriage from state court decisions striking down marriage laws that exclude gay and lesbian couples. So far that has happened in just one state, Massachusetts, where same-sex marriages became legal in 2003, although court cases are pending in other states.
To become part of the Constitution an amendment needs approval from at least two-thirds of the Senate (67 of the 100 members), at least two-thirds of the House (290 of the 435 members) and three-fourths of the states (38 of the 50 states), or by a convention called by three-fourths of the states.
In the nearly 220 years since the Constitution was written, only 27 amendments have made it through this arduous approval process, the most recent in 1992 governing the timing of changes in congressional compensation. No amendment has been approved by a convention.
CNN's Dana Bash contributed to this report.