WASHINGTON – Three federal judges reacted skeptically Monday to a conservative group that wants to air an advertisement around election time singling out Maine’s two U.S. senators on the issue of same-sex marriage.

The Christian Civic League of Maine is challenging a provision of federal law that bars corporate and union treasury funds from being used to influence campaigns right before an election.

The league’s proposed radio ad represents grass-roots lobbying rather than electioneering, said James Bopp, an attorney for the conservative group that claims its free speech rights are harmed by the law.

In Maine’s election primary, scheduled for June 13, Sen. Olympia Snowe, a Republican, is running unopposed. Maine’s other senator, Republican Susan Collins, doesn’t face re-election until 2008.

The Federal Election Commission said that allowing the ad to run would seriously erode what has been a clear-cut rule in the campaign fundraising reform law sponsored by Sens. John McCain, R-Ariz., and Russell Feingold, D-Wis.

The provision prohibits corporations or interest groups from airing advertisements that name candidates within 30 days of a primary election and 60 days before general elections.

The Christian Civic League “is basically asking for a blank check” to run ads that the law prohibits, said Daniel Ortiz, an attorney for five members of Congress who supported the reform legislation.

The three judges who heard the arguments expressed strong doubts that the ad could be broadcast as worded and still comply with the Bipartisan Campaign Reform Act of 2002.

“Why is it necessary to have the senators’ names in there?” asked U.S. District Judge Colleen Kollar-Kotelly.

U.S. District Judge Louis Oberdorfer suggested the ad may be both First Amendment-protected lobbying and, at the same time, electioneering that is barred by the 2002 law.

Appeals Court Judge Judith Roberts asked whether the ad would comply with the law if the names of the senators were removed. FEC attorney David Kolker said such a move would allow for “the kind of mischief” that led to the law’s enactment in the first place.

Rogers and Kollar-Kotelly are Clinton appointees, and Oberdorfer is a Carter appointee.