WASHINGTON - Estimates of the number of graves that might be affected by mix-ups at Arlington National Cemetery grew from hundreds to as many as 6,600 on Thursday, as the cemetery's former superintendent blamed his staff and a lack of resources for the scandal that forced his ouster.

John Metzler, who ran the historic military burial ground for 19 years, said he accepts "full responsibility" for the problems.

But he also denied some of the findings by Army investigators and suggested cemetery employees and poor technology were to blame for remains that may have been misidentified or misplaced. He said the system used to track grave sites relied mostly on a complicated paper trail vulnerable to error.

"Personally it is very painful for me that our team at Arlington did not perform all aspects of its mission to the high standard required," he told a Senate panel. He was subpoenaed to testify.

Metzler and his deputy, Thurman Higginbotham, were forced to retire after Army investigators found that as many as 211 graves were unmarked or misidentified. The report by the Army Inspector General's office accused Metzler of repeatedly failing to ensure burials were being done properly and of failing to respond after unmarked graves were discovered.

Sen. Claire McCaskill, chairwoman of an oversight panel on the Senate Homeland Security and Government Reform Committee, said Thursday that her investigation has revealed far higher estimates of the number of graves affected. McCaskill, a Missouri Democrat, said she believes that between 4,900 and 6,600 graves may be unmarked or mislabeled on cemetery maps.

Kathryn Condon, who was hired to fix the cemetery's problems, testified that the Army was still trying to determine exactly how many burial sites could be affected. But, she said, "I am confident there are probably other map errors" beyond the 211 sites initially identified by Army investigators.

Metzler said an inspector general finding that more than 100 graves lacked a headstone or burial card was not entirely accurate and that it was mostly internal working maps used by cemetery employees that were mislabeled.

Metzler insisted that discrepancies on those maps wouldn't necessarily affect operations.

He also said any problems that came up over the years were quickly fixed and suggested he was surprised by the findings of the Army's Inspector General.

His testimony angered and confused lawmakers.

"The notion that you would come in here and act like you didn't know about it until a month ago is offensive. You did know about it, and you did nothing," McCaskill said.

A visibly frustrated Sen. Scott Brown abruptly ended his questioning.

"I'd have a lot of fun with you in a deposition because I don't think we're getting straight talk here," said Brown, R-Mass.

Higginbotham testified in general about his tenure at the cemetery but left the hearing early after asserting his Fifth Amendment right not to respond to many of the lawmakers' more pointed questions.

As deputy superintendent who ran day-to-day operations at the cemetery, Higginbotham is accused of directly contributing to the chaos. While Army officials have described Metzler as an ineffective manager who turned a blind eye to the cemetery's problems, investigators accuse Higginbotham of botching contracts and creating an "unhealthy organizational climate" for employees.

When asked whether he was aware of problems at the cemetery, Higginbotham said: "It was always conceptual that anything done by hand for 40-plus years, that there would have to be some errors somewhere."