A lawsuit filed in June by Nader asked U.S. District Judge Patti Saris to invalidate Federal Election Commission regulations that allow corporate sponsorship of the debates.

Scott Lewis, who represents Nader and his co-plaintiffs, said the FEC regulations are "inconsistent with the plain terms of the law" that bars corporate funding of campaigns.

He said the scheduled October debates are essentially "paid advertisements subsidized by corporate contributors for those candidates who participate in them."

Stephen Hershkowitz, an FEC attorney, argued that the regulations were consistent with Congress' intent when it wrote the law.

He noted that the law already bars corporations from contributing to campaigns and said the plaintiffs -- including celebrity supporters Susan Sarandon and Phil Donahue and other Green Party candidates -- were trying to further restrict companies.

Saris took the case under advisement.

Corporations have spent millions to sponsor past debates. This year, AT&T, Anheuser-Busch and Sun Microsystems, are among companies making tax-deductible contributions to the nonprofit Commission on Presidential Debates.

The commission has proposed presidential debates in Boston, St. Louis and Winston-Salem, N.C., and one vice presidential debate in Danville, Ky. Texas Gov. George W. Bush, the Republican nominee, and Vice President Al Gore, the Democratic nominee, have yet to agree to the schedule.

The commission is co-chaired by former Democratic National Committee Chairman Paul Kirk and former Republican National Committee Chairman Frank Fahrenkopf Jr.

Janet Brown, executive director of the commission, said it has filed a "friend of the court" brief in the case declaring that it is in compliance with FEC and Internal Revenue Service requirements.

In January, the commission ruled that only candidates with at least 15 percent support in national polls could participate. That means Nader -- who remained in single digits in the most recent national surveys -- may be excluded from the debates.