WASHINGTON - Seeking to overturn the nation's month-old campaign finance law, opponents of the new rules told a federal court yesterday that the limits trample the free-speech rights of political parties and urged the judges to overturn the hard-won statute.

Bobby Burchfield, an attorney representing the Republican National Committee, told a special three-judge panel that the law, which took effect Nov. 6, could "stifle" democracy by limiting the parties' ability to educate voters and encourage people to go to the polls.

The campaign finance law, approved by Congress in March, bans the national political parties from accepting "soft money," the previously unregulated and unlimited donations from corporations, labor unions, other organizations and wealthy individuals that have played an increasingly important part in elections by financing issue-oriented advertising.

Although the money technically could not be used to back specific candidates under old rules, it usually was spent supporting or attacking issues linked closely to a candidate. "Hard money" contributions are used to directly promote candidates.

In 2000, soft money contributions to both parties reached $487 million.

Sen. Mitch McConnell, a Kentucky Republican, and dozens of groups - including the RNC, California Democratic Party, AFL-CIO, American Civil Liberties Union, U.S. Chamber of Commerce and National Rifle Association - contend that the restrictions violate constitutional rights to free speech.

"By cutting off those funds, the law prevents the parties from getting out their views on issues and candidates, which is a violation of their First Amendment rights," Burchfield told the panel, which will decide if the law violates the rights of candidates, political parties and advocacy groups.

Attorney Kenneth W. Starr, the former Whitewater special prosecutor who is representing McConnell, argued that the law would devastate the nation's political system by transferring money and influence from the national parties to a network of secretive special interest groups that will still be able to spend soft money.

Instead of reducing corruption, he said, it could make lawmakers more beholden to special interests - while making it harder to challenge incumbent lawmakers.

But supporters of the law told the court that before the new contribution limits, million-dollar donations had turned the political process into a "pay-to-play" system that eroded Americans' trust in democracy.

"The campaign finance law sought to fix a broken system that reeked of influence peddling," said Roger Whitten, a lawyer representing Sens. John McCain, an Arizona Republican, and Russell D. Feingold, a Wisconsin Democrat, who fought for years to pass the campaign finance overhaul.

Whitten said that during calls to corporations and unions in search of large donations, politicians were instructed by their national parties to "inform" the potential contributors of legislation pending in Congress that could affect their business.

Richard Bader, associate general counsel of the Federal Election Commission, said the old rules had given the country the "spectacle" of big donors sleeping in the Lincoln bedroom at the White House.

After a ruling by the special three-judge panel, the case will go directly to the Supreme Court, where supporters expect Solicitor General Theodore B. Olson to defend the law.

McCain said in a statement yesterday that he was confident the law would withstand the legal challenges.