WASHINGTON — Democratic leaders hinted yesterday that compromise may be needed to get wavering lawmakers on board for a bill to make union organizing easier.

The Democrats insisted they are not losing support, but acknowledged that some changes might be needed.

The comments came as the Employee Free Choice Act was formally introduced in the House and Senate, intensifying the already heated debate between business groups that oppose the measure and labor groups that consider it their top priority.

Iowa Sen. Tom Harkin, a lead sponsor of the bill, said his colleagues are talking about "certain modifications," but no agreement has been reached.

"There might be some amendments that don't destroy the underpinnings of the bill, maybe provide for better enforcement," Harkin said. "That type of thing might be acceptable."

The bill would reform labor laws by allowing workers to form unions by simply signing a card or petition, removing an employer's right to demand a secret ballot vote. It also would impose stronger penalties on employers who violate labor laws and allow for arbitration to settle contract disputes.

"If we want to have a fair and sustainable recovery from this economic crisis, we must give workers the ability to stand up," said Rep. George Miller, D-Calif., chief sponsor of the House bill and chairman of the House Education and Labor Committee.

Unions say the bill would discourage employers from firing or harassing workers who seek to organize and claim increased union membership would boost wages and help the economy.

At a hearing before the Senate Health, Education and Labor Committee, Republicans called it a job-killing measure that would leave workers open to union intimidation.

"There is no evidence that forced unionization will do anything to assist the middle class and deliver economic security for workers," said Sen. Johnny Isakson, R-Ga.

An identical version of the bill cleared the House easily two years ago, but could not muster 60 votes to get past a Republican filibuster in the Senate.