WASHINGTON  Senate Republicans on Wednesday blocked a measure intended to overturn a Supreme Court decision limiting pay discrimination suits in a politically charged vote certain to be replayed in the presidential and Congressional campaigns.

By a vote of 56 to 42, the Senate fell four votes short of the 60 required to begin consideration of the Lilly Ledbetter Fair Pay Act, named for an Alabama woman who lost a case against the Goodyear Tire and Rubber Company when the court found she not did file her complaint in time. Ms. Ledbetter had been paid as much as 40 percent less than her male counterparts doing the same job, according to her allies.

The political elements of the debate were unmistakable. Unable to reach an agreement with Republicans, Democrats did not convene the Senate until 5 p.m. so their two presidential candidates  Senators Hillary Rodham Clinton of New York and Barack Obama of Illinois  could return from the campaign trail. Both spoke in favor of the legislation.

The campaign arm of Senate Democrats quickly issued news releases attacking Republicans up for re-election who opposed the procedural vote. And Democrats warned Republicans that they would hear from voters on an issue of major import to women as they accused Republicans of missing an opportunity to help victims of pay discrimination pursue justice in court.