* Aging activists broke into nuclear bomb facility in July
* Lawmakers concerned security inadequate at other facilities too
WASHINGTON, Sept 13 (Reuters) - Top Energy Department officials and contractors they employ need to be held accountable for an unprecedented security lapse in July at a facility that stores enriched uranium used to make nuclear bombs, top lawmakers on the House Armed Services Committee said on Thursday.
An 82-year-old nun and two other anti-nuclear activists cut through several fences to reach the heavily guarded Y-12 complex in Oak Ridge, Tennessee, and went unchecked as they vandalized the building's exterior, sparking a series of investigations at the Energy Department and in Congress.
Michael Turner, chairman of the House of Representatives Strategic Forces Subcommittee, and Loretta Sanchez, the top Democrat on the panel, wrote to President Barack Obama on Thursday to say they were concerned that security was inadequate at the facilities in the nation's nuclear weapons complex.
"Lapses at every level in terms of process, personnel and accountability could have allowed a disaster. We believe these issues may not be limited to Y-12," Turner and Sanchez told Obama, asking him to pay "personal attention" to the issue.
An internal Energy Department watchdog found guards ignored motion sensors because they were routinely triggered by wildlife, and a security camera that should have shown the break-in had been broken for about six months.
The head of the National Nuclear Security Administration told lawmakers on Wednesday that government oversight should have caught the problems.
"If the facility had actually been under attack and all these systems had failed, we would have had an absolute catastrophe," Turner said at the beginning of a Capitol Hill hearing on Thursday.
Turner, a Republican, said the administration needed to follow the example set by then-Defense Secretary Robert Gates in 2008, when he fired the two top officials at the Air Force after mistakes involving nuclear weapons security.
"As the Y-12 investigations proceed, I expect to see similarly strong actions," Turner said.
In 2008, authorities in Taiwan revealed that the Air Force had mistakenly shipped nuclear fuses two years earlier, an error that went unnoticed by the Pentagon.
The disclosures came months after an Air Force bomber carrying six nuclear warheads flew across the United States.
Current Energy Department investigations include a review of contracts held by Babcock & Wilcox Co, which runs the facility, and WSI Oak Ridge, owned by G4S, which provides security.
At Thursday's hearing, most of which was classified, Deputy Energy Secretary Daniel Poneman said the department would "leave no stone unturned" in trying to determine how systems failed.