WASHINGTON — Senate Republicans killed legislation Wednesday aimed at removing limits on how long workers can wait before suing their employers for pay discrimination.

Democrats, speaking to key constituencies of women, minorities and swing voters this election year, said they weren't finished trying to pass the bill.

"Women of America: Put your lipstick on, square your shoulders, suit up" and get ready to fight, Sen. Barbara Mikulski, D-Md., said moments after the bill's opponents denied supporters the 60 votes needed to proceed to full debate and a vote on passage. "The revolution starts tonight."

Debate on the legislation, which was proposed in response to a Supreme Court decision last year, was steeped in election-year politics and shadowed by a White House veto threat.

Democratic presidential rivals Hillary Rodham Clinton and Barack Obama swung through Washington to speak from short, prepared statements in favor of the legislation. It was the first time in months that both candidates spoke on the Senate floor, an indication of the bill's importance to voters the two are fighting for in their ongoing battle for their party's nomination.

But Republicans were unified against it enough to muster 42 votes to supporters' 56 votes. The bill passed the House in July, 225-199.

The presumed Republican presidential nominee, Sen. John McCain, who was out campaigning and did not vote, said he opposed the measure.

Watching the vote from the Senate visitors' gallery overhead was Lilly Ledbetter, an Alabama woman whose discrimination case was thrown out by the Supreme Court and for whom the legislation is named.

Ledbetter was a supervisor at the Goodyear Tire & Rubber Co.'s plant in Gadsden, Ala., who sued for pay discrimination just before retiring after a 19-year career there. By the time she retired, Ledbetter made $6,500 less than the lowest-paid male supervisor and claimed earlier decisions by her supervisors kept her from making more.

The Supreme Court voted 5-4 last May 29 to throw out her complaint, saying she had waited too long to sue. Under the justices' decision, which they said was based on the 1964 Civil Rights Act, an employee must sue within a 180-day deadline of a decision involving pay if the employee thinks it involved race, sex, religion or national origin.

That opens the door for corporations to discriminate, Democrats said. The legislation would restart the statute of limitations for pay discrimination lawsuits each time an employee gets a paycheck affected by sexism or racism.