Veterans Affairs chief Jim Nicholson, who was forced to defend the Bush administration's handling of people injured in battle after revelations of shoddy health care at Walter Reed Army Medical Center, announced Tuesday he is resigning.

The 69-year-old Nicholson, who is returning to the private sector, has been head of the VA since February, 2005. Before that, he was U.S. ambassador to the Vatican and chairman of the Republican National Committee.

He is the latest in a lengthening line of senior officials heading for the exits in the final 1 1/2 years of President Bush's administration.

Nicholson most recently has overseen a vast network of 1,400 hospitals and clinics, which provide supplemental care and rehabilitation to 5.8 million veterans.

Earlier this year, the VA was embarrassed by revelations of poor health care at Walter Reed for veterans wounded in Iraq and Afghanistan. Nicholson was named by President Bush to lead an interagency task force of seven Cabinet secretaries to determine what could be done immediately to improve veterans' care.

Nicholson defended the VA, but acknowledged there is room for improvement.

"When you're seeing over 1 million patients a week, you have to be very good, and if there is any one patient who doesn't get the care that they deserve, that's unacceptable," Nicholson said in March.

"The American people can feel very good about the health care system that their VA is providing to veterans," Nicholson said then, "but if there is a case where a veteran gets lost in the system, or suffers anxiety or their family does as a result of something we're not doing, that is unacceptable."

Sen. Patty Murray, a Washington Democrat who sits on the Veterans Affairs Committee, said that "we need the president to send us a serious nominee to fill the job. That means a truthful advocate for veterans, not an apologist for this administration's failures to plan."

Nicholson just this week pledged to add mental health services at more than 100 VA medical centers. In addition, the VA is adding new VA-run Vet Centers, hiring more suicide prevention coordinators and hosting state mental health conferences to facilitate collaboration of veterans services.

Nicholson, a decorated Vietnam veteran who retired as a colonel in the Army Reserve, said he would leave by Oct. 1.

Nicholson also had some tense moments explaining his agency's stewardship of veterans issues after it was learned that VA computer files with personal data, including Social Security numbers, for 26.5 million veterans and military troops, were missing.

Burglars had stolen computer equipment from a data analyst's Maryland home on May 3, 2006. Law enforcement officials recovered the laptop and hard drive about two months later after being tipped by an informant who had heard about a $50,000 reward and knew where they could be found.

Called to account at Capitol Hill hearings, Nicholson said he was angry that he hadn't been told about the burglary until nearly two weeks after it happened.

Nicholson acknowledged at the time that officials including Deputy Secretary of Veterans Affairs Gordon Mansfield knew about the incident earlier, but would not say whether Mansfield should be punished, citing a need for a full investigation.

"As a veteran, I am outraged. Frankly I'm mad as hell," Nicholson said, pledging strong action against those responsible. "I can't explain the lapses of judgment on the behalf of my people. We will stay focused on these problems until we get them fixed."

Nicholson was National Republican Committee chairman from 1997 through the 2000 elections.

Within months of taking office at the VA, he had to deal with a $1 billion shortfall at the agency, requiring the Bush administration to appeal to Congress for emergency spending.

Republicans blamed the shortfall on unexpected health care demands from veterans. But Democrats said it was an example of what they said was the administration's inadequate planning for the war in Iraq.