WASHINGTON — The families of four private guards whose bodies were burned and dragged through the streets by a mob in Iraq told Congress yesterday that the security company that hired them failed to provide armored vehicles and other promised protections.

The guards’ families have sued the company, Blackwater USA, telling a House hearing it was the only way they can learn all the circumstances of the deaths. Blackwater and several Republican lawmakers said the lawsuit should not be argued at a congressional hearing.

The deaths of the four, all former members of the military, brought to American television some of its most gruesome images of the Iraq war. A frenzied mob of insurgents ambushed a supply convoy the guards were escorting through Fallujah on March 31, 2004. The men were attacked, their bodies mutilated; two of the corpses were strung from a bridge.

At the hearing, the mother of Stephen Helvenston, Kathryn Helvenston-Wettengel, read a statement on behalf of the families. She stopped several times to collect herself as she recounted the emotional day.

She said the security guards were denied armored vehicles, heavy weapons, and maps for their convoy routes, and that the rear gunners were removed from vehicles to perform other duties.

“Blackwater gets paid for the number of warm bodies it can put on the ground in certain locations throughout the world,” she said. “If some are killed it replaces them at a moment’s notice.”

Ms. Helvenston-Wettengel said her son was alive when Iraqis tied him to his vehicle and dragged him through the streets. He eventually was decapitated.

In a statement prepared for House Oversight and Government Reform Committee, Blackwater USA general counsel Andrew Howell said lawyers for the family members were using the hearing for their own purposes and that the case should be heard in court, not in Congress.

Mr. Howell said the hearing should not delve into an “incomplete and one-sided exploration of a specific battlefield incident.”

Rep. Darrell Issa, a Republican of California, said he did not believe the testimony was germane to a house committee scrutinizing American companies with Iraq contracts. He pressed the witnesses on whether their lawyers wrote their statement, but Ms. Helvenston-Wettengel said each of the four women at the hearing wrote a portion of the statement.

The three men killed in addition to Helvenston — a former Navy SEAL — were a former Army Ranger represented by his daughter Kristal, Wesley Batalona; Michael Teague, who was formerly in an Army helicopter unit, represented by his widow, Rhonda, and Jerry Zovko, who was a former Army Ranger represented by his mother, Donna.

The committee also is looking into Blackwater’s contract to provide security services in Iraq. After numerous denials, the Pentagon has confirmed that Blackwater provided armed security guards in Iraq under a subcontract that was buried so deeply the government at first couldn’t find it.

The secretary of the Army on Tuesday wrote two Democratic lawmakers that the Blackwater USA contract was part of a huge military support operation by run by Halliburton Co. subsidiary KBR. Vice President Cheney ran Halliburton before he took office.

Several times last year, Pentagon officials told inquiring lawmakers they could find no evidence of the Blackwater contract. Blackwater, of Moyock, N.C., did not respond to several requests for comment.