WASHINGTON - Top members of President Bush's national security team are leaving in one of the earliest waves of departures from a second-term administration - nearly two years before Bush's time ends.

At least 20 senior aides have retired or resigned from important posts at the White House, Pentagon and State Department in the last six months.

Some have left for lucrative positions in the private sector. Some have gone to academic or charitable institutions. The latest was Deputy National Security Adviser J. D. Crouch, who spoke favorably of Bush's policies as he announced he was leaving last week.

Turnover is normal as an administration nears its end, but "this is a high number," said Paul Light, a professor of public service at New York University and an expert on government.

"You would expect to see vacancies arise as things wind down," he said, "but it's about six months early for this kind of a mass exodus."

One reason may be that Vice President Cheney will not run to succeed Bush in 2008, setting the stage for wholesale changes at all levels of government no matter who wins the election. Also, several of the departures were not voluntary.

Some officials, speaking privately, said some people might be leaving to avoid being associated with the Iraq war.

At the White House, four top officials have stepped down: Crouch; Meghan O'Sullivan, another deputy national security adviser who worked on Iraq; Tom Graham, the senior director for Russia; and Victor Cha, the point man for Asian affairs.

O'Sullivan's departure has set off a search for a "war czar" to oversee operations in Iraq and Afghanistan, a job reportedly turned down by a number of senior or retired generals.

Graham's resignation comes as tensions with Russia rise over U.S. missile-defense plans in Europe, and Cha leaves amid concerns over North Korea's failure to comply with deadlines to eliminate its nuclear- programs.

Former Defense Secretary Donald H. Rumsfeld resigned under fire in November and is not included in the list of 20.

His close associate and chief of intelligence, Stephen Cambone, followed him out the door, as did Peter Rodman, the assistant defense secretary for international security affairs. Army Secretary Francis Harvey was fired over shoddy conditions in outpatient care at Walter Reed hospital.

Another Pentagon official, Richard Lawless, the senior policy coordinator for Asia, is expected to leave this summer.

The State Department has been hit hardest, with at least five so-called principals - people in the top four tiers of the bureaucracy - stepping down.

Light said the diplomatic departures appeared to demonstrate a feeling that the administration was running out of time for foreign-policy accomplishments despite Secretary of State Condoleezza Rice's perseverance.

"They reflect a decline in the Bush foreign-policy agenda," he said. "No matter how hard Condi Rice works, this administration's foreign policy has pretty much run its course."

Deputy State Department spokesman Tom Casey said the departures were not unusual.

"This is a normal part of life at the department," he said. "It's part of a cycle where people pursue other opportunities at times that are appropriate for them, but we continue to be blessed with exceptional people in the building for our important diplomatic work."

Some of the Key Departures

Some of the most prominent senior members of President Bush's national security team who have resigned or retired in the last six months:

J.D. Crouch, deputy national security adviser

Meghan O'Sullivan, deputy national security adviser

Victor Cha, National Security Council Asia expert

Stephen Cambone,

Pentagon intelligence chief

John Bolton, U.S. ambassador to the U.N.

Robert Joseph, undersecretary of state

for arms control and international security

Philip Zelikow, State Department counselor

John Hillen, assistant secretary of State for

political and military affairs

Henry Crumpton, State's counterterrorism coordinator

Stephen Krasner, State's policy planning director

Barry Lowenkron,

assistant secretary of

state for democracy, human rights and labor

Dina Habib Powell,

assistant secretary of

state for educational and cultural affairs

SOURCE:: Associated PressEndText