The prospects for legislation to establish a shield law for reporters appeared dim as the measure’s sponsor said he was unsure he would vote to move it forward in the Senate on Wednesday.

Arlen Specter , R-Pa., said Tuesday that he may not vote to limit debate on a motion to call up his own bill out of anger over procedural maneuvers used by Majority Leader Harry Reid , D-Nev., to limit amendments that Republicans can offer to energy speculation legislation.

“I’m sort of caught in the middle on that,” Specter said after an appearance at the Heritage Foundation. “I’ve worked so hard on the reporter’s shield bill but I’m strongly opposed to what Reid is doing on amendments.”

Specter’s bill would provide legal protections for journalists to protect the identity of anonymous sources in some instances.

The potential defection of the measure’s sponsor and lead Republican supporter is likely to make taking up the bill all the more difficult. If anything, any defection makes it tougher to reach the 60-vote threshold require to move the bill forward.

Specter has made several changes to his bill in recent weeks, in a bid to win over critics within his own party. Supporters fear that it could end up being greatly watered-down, making it difficult for reporters to protect sources or information the government demands under the rubric of national security.

The House passed its version in October by a vote of 398-21, but Specter’s bill would be the vehicle for the legislation to go to President Bush.

The Bush administration opposes the bill.