A federal judge refused Friday to dismiss a defamation case against Rep. John P. Murtha and ordered the Pennsylvania Democrat to give a sworn deposition in the case.

A Marine Corps sergeant accuses the 16-term congressman of falsely accusing him of "cold-blooded murder and war crimes" in connection with the deaths of Iraqi civilians.

The Justice Department wanted the case dismissed because Murtha was acting in his official role as a lawmaker. Assistant U.S. Attorney John F. Henault said the comments were made as part of the debate over the war in Iraq.

U.S. District Judge Rosemary M. Collyer said the congressman might be right, but said she won't know for sure unless Murtha explains himself. She did not set a date for Murtha's testimony but said she would also require him to turn over documents related to his comments.

Collyer said she was troubled by the idea the lawmakers are immune from lawsuits regardless of what they say to advance their political careers.