WASHINGTON ?  The scandal over conditions at the Walter Reed Army Medical Center claimed its second victim Friday when Secretary of the Army Francis Harvey handed in his resignation to his boss, Defense Secretary Robert Gates.

"The problems at Walter Reed appear to be problems of leadership," Gates told reporters at the Pentagon during an unscheduled appearance.

Harvey's resignation follows the departure of a top Army official on Thursday. Army Maj. Gen. George W. Weightman was relieved of his command after senior officials said they lost trust and confidence in his leadership abilities. Weightman, a two-star general, oversaw the North Atlantic Regional Medical Command and Walter Reed.

Shortly after Gates' announcement, the Army announced that Maj. Gen. Eric Schoomaker will be Weightman's replacement. Up to now, Schoomaker has been in charge of the U.S. Army Medical Research and Materiel Command at Fort Detrick, Md., the Army said.

"Gen. Eric Schoomaker has the right blend of leadership, professional expertise and personal experience for this position," Army Vice Chief of Staff Gen. Richard Cody said in a news release.

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In the brief appearance Friday, Gates said he was "disappointed" in how Army officials have handled the problems at Walter Reed, but did not take any reporters' questions.

"I am disappointed that some in the Army have not adequately appreciated the seriousness of the situation pertaining to outpatient care at Walter Reed. Some have shown too much defensiveness and have not shown enough focus on digging into and addressing the problems," Gates said.

Harvey has been the Army secretary since November 2004. Gates said Harvey will depart March 9. Gates said the Army under secretary, Pete Geren, will become acting secretary until Bush nominates a permanent replacement.

Gates' announcement came on the same day that President Bush ordered a comprehensive review Friday of conditions at the nation's military and veteran hospitals.

The White House said the president would name a bipartisan commission to assess whether problems at Walter Reed exist at other facilities.

The commission to be named by Bush is separate from a review panel appointed by Gates. Gates' panel will investigate outpatient care at Walter Reed and the National Naval Medical Center in Bethesda and allegations of poor quality-of-life conditions for soldiers injured in Iraq and Afghanistan. Gates' independent panel began its work on Thursday .

The presidential panel will look at all of the nation's military and veteran facilities, White House deputy press secretary Dana Perino said.

Officials were forced to respond after news articles drew concerns of a deteriorating environment at the 113-acre institution that is the Army's top medical facility. Building 18 — which houses hundreds of soldiers recovering from battle wounds — was reported to have mold and soiled carpets as well as mouse and cockroach infestations among other problems.

Also Friday, the House Committee of Oversight and Government Reform issued a subpoena to force Weightman to testify before lawmakers.Weightman was scheduled to come before the committee but the Army refused to authorize him after he was relieved of command. And on Monday, congressional hearings are set to begin on the matter.

Bush will devote his weekly radio address — to be broadcast Saturday — to the problems of veterans' care, according to excerpts released Friday. A full text also was to be released later Friday.

The administration's response came amid growing outrage about the poor treatment of some veterans — and the prospect that it could backfire on the White House.

"One of my most solemn experiences as president is visiting men and women recovering from wounds they suffered in defense of country," Bush said in his prepared address. "Spending time with these wounded warriors is also inspiring because so many of them bring the same courage they showed on the battlefield to their battle for recovery."

Sen. Claire McCaskill, D-Mo., quickly fired off a statement saying Harvey's resignation is a good start but not enough to fix the problems, and she renewed her call for the firing of the Army's top medical official, Army Medical Command, Lt. General Kevin Kiley.

"The fact remains that the general in charge of the medical command knew of the problems and then diminished them when they became public. He was responsible for the command culture that caused these problems and should be relieved of his command," McCaskill said.

The Associated Press contributed to this report.