WASHINGTON — A Marine Corps sergeant under investigation in connection with the deaths of 24 Iraqi civilians in Haditha is accusing Rep. John Murtha of defaming him in public comments about the case.

Lawyers for Staff Sergeant Frank Wuterich, 26, argue in a suit filed yesterday in federal court that Mr. Murtha falsely accused Sergeant Wuterich “of cold-blooded murder and war crimes” — although the lawyers acknowledged during a news conference that Mr. Murtha named Sergeant Wuterich’s squad, not Sergeant Wuterich personally, when speaking with reporters.

On May 17, Mr. Murtha said he had learned from Marine Corps officials that innocent Iraqis had been killed “in cold blood.”

Mr. Murtha, a Democrat of Pennsylvania, issued a statement yesterday saying he doesn’t blame Sergeant Wuterich for “lashing out.”

“When I spoke up about Haditha, my intention was to draw attention to the horrendous pressure put on our troops in Iraq and to the cover-up of the incident,” Mr. Murtha, a 16-term congressman who was campaigning for re-election yesterday in his hometown of Johnstown, Pa., said.

The suit maintains that Pentagon officials “who have briefed or leaked information to Murtha deliberately provided him with inaccurate and false information” and that the congressman subsequently “has made repeated statements … that are defamatory” to Sergeant Wuterich and his fellow Marines.

The suit accuses Mr. Murtha of spreading “false and malicious lies” about Sergeant Wuterich and his squad that were “intended to serve his own private purpose and interests” and says Mr. Murtha’s comments “have been reproduced by countless third parties throughout the world.”

It says many of Mr. Murtha’s remarks were made outside his “scope of employment as a congressman.” Mr. Murtha, a former Marine and decorated Vietnam War veteran, has been a leading proponent of withdrawing American forces from Iraq.

The claim for libel and invasion of privacy seeks damages to be determined, but not less than $75,000.

An attorney for Sergeant Wuterich, Mark Zaid, said during a news conference that the suit was not about money or politics.

“This case … is about truth, honor, and accountability, and Congressman Murtha, who we believe has acted out of his scope as a congressman,” Mr. Zaid said.

The suit details Sergeant Wuterich’s account of what happened on November 19, 2005, in Haditha, a story he has told through his lawyers previously.

Sergeant Wuterich maintains that several civilians were killed when his squad pursued insurgents firing at them from inside a house after a roadside bombing that killed one Marine. He describes a house-to-house hunt that went wrong in the midst of a confusing battlefield, but he has denied through his attorneys any vengeful massacre.

Sergeant Wuterich and other Marines from his 3rd Battalion, 1st Marine Regiment, are under investigation by the Naval Criminal Investigation Service. A parallel investigation is looking at whether officers at higher levels in the chain of command covered up the facts.

No one has been charged in the case.

A Pentagon official told the Associated Press yesterday that evidence collected on the deaths of 24 Iraqis in Haditha supports accusations that American Marines deliberately shot the civilians, including unarmed women and children.

The court case was first reported late Tuesday on the Washington Post’s Internet site.