The leaders of a congressional committee investigating the Dover Air Force Base mortuary said Thursday that they would broaden their probe to include all military burial practices over the past decade, including reports that partial remains of hundreds of war dead were incinerated and dumped in a Virginia landfill.

Rep. Darrell Issa (Calif.) and Rep. Elijah Cummings (Md.), the top Republican and Democrat, respectively, on the House Oversight and Government Reform Committee, said they found “appalling” revelations in The Washington Post on Thursday that the Air Force shipped incinerated remains from at least 274 troops to the King George County Landfill before ending the practice in 2008.

The lawmakers pressed the Pentagon for “full cooperation and transparency” in the investigation and said they would examine the military’s “practices in handling remains at all facilities since January 2002.” Legislative officials said that would include Arlington National Cemetery and other military cemeteries as well as Dover Air Force Base, the main entry point for the nation’s war dead.

“The Tomb of the Unknown is one of our nation’s most hallowed places, guarded around the clock — regardless of weather — every day of the year,” Issa and Cummings said in a joint statement. “We owe this spirit of reverence not only to the unknown service members entombed at Arlington, but to all those who wear the uniform to protect and defend our freedom.”

The House Oversight Committee opened its investigation last month after reports of “gross mismanagement” and missing body parts at the Dover mortuary. Since then, the panel has made clear that it would also examine the mortuary’s past practice of dumping incinerated remains in a Virginia landfill, as well as lingering problems at Arlington.

The lawmakers’ concerns contrasted with statements Thursday from the Pentagon, where officials said they were confident in the Air Force’s handling of fallen service members despite several embarrassing disclosures in the past month.

Defense Secretary Leon E. Panetta supports the Air Force’s handling of the scandals, spokesmen from the Pentagon said. Panetta also agrees with the Air Force’s decision not to notify relatives of the 274 fallen service members whose body fragments were incinerated and secretly dumped in the landfill, Navy Capt. John Kirby, a Pentagon spokesman, told reporters.

“The secretary is comfortable with the way the Air Force has handled this,” Kirby told reporters at a news conference.

Kirby said there were “real constraints” that restrict the Air Force from notifying relatives of the dead troops. Air Force officials said each of the families signed forms stipulating that they did not wish to be notified if additional remains were subsequently recovered or identified.

The forms authorized the military to dispose of those remains in an “appropriate manner.” The families were not told that the remains would be cremated, incinerated and dumped in a landfill.

Lt. Gen. Darrell D. Jones, the Air Force’s deputy chief of staff for personnel, said the military wanted to spare relatives additional anguish. “To open up that wound, that would be cruel.”

He said the Air Force would confirm for family members whether their loved one’s partial remains were put in the landfill if they came forward and requested the information.

Last month, Panetta ordered a review of operations at the Dover mortuary after investigations by the Air Force inspector general and the Office of Special Counsel, a federal agency that handles whistleblower complaints, documented cases of missing body parts and other problems.

Panetta “is committed, obviously, to the principle that our fallen heroes and their families deserve the very best in how they are treated,” said George Little, the Pentagon press secretary. “The secretary feels that the Air Force has been forthcoming with information related to Dover.”

Joe Davis, the national spokesman for Veterans of Foreign Wars, said the latest reports suggest the military hasn’t been transparent. By contrast, he argued, the Defense Department was relatively forthcoming about problems at Arlington after initial reports that remains had been mishandled there.

At Dover, he said, the investigation hasn’t moved fast enough, and there are fears that more worrisome findings could emerge.

“Here, you continue to pull back the layers of the onion and there’s still an onion there,” Davis said.

Staff writer Jason Ukman contributed to this report.