WASHINGTON - The State Department official responsible for overseeing Blackwater USA and other private security contractors in Iraq resigned abruptly Wednesday.

Richard J. Griffin, who has been the director of the department's diplomatic security bureau since June 2005, faced stiff criticism from Congress over his handling of a Sept. 16 shooting episode involving Blackwater security guards during which Iraqi investigators say 17 Iraqis were killed and other acts of violence were perpetrated by the State Department's contractors.

A special panel appointed to investigate the handling of diplomatic security in Iraq found a glaring lack of oversight and accountability that was hindering the American diplomatic and military mission there.

The FBI and a joint American-Iraqi board are also investigating the Sept. 16 shooting and the operations of armed private guards in Iraq.

Secretary of State Condoleezza Rice quickly accepted Griffin's resignation, which is effective Nov. 1. "Secretary Rice is grateful to Ambassador Griffin for his record of long exemplary service to the nation," said Sean McCormack, the State Department spokesman.

Rice is scheduled to appear today before the House Oversight and Government Reform Committee, which has been investigating problems with Blackwater and other security contractors in Iraq.

The committee's chairman, Rep. Henry A. Waxman, D-Calif., said Wednesday, "Mr. Griffin's resignation is another indication that the State Department's efforts in Iraq are in disarray."

Griffin directed a little-known State Department bureau responsible for protection of American facilities and diplomats overseas. It employs 1,450 special agents who serve as bodyguards for ambassadors and other dignitaries abroad but found itself unable to handle the security demands brought on by the wars in Afghanistan and Iraq.

It turned to private American security companies such as Blackwater and DynCorp International, which handle the bulk of guard work for American civilians in those two countries.

In his two-paragraph letter of resignation to President Bush, Griffin cited his 36 years in government service, which has included senior posts in the Secret Service and the Department of Veterans Affairs. He did not mention Blackwater or Iraq, nor cite a specific reason for leaving. He wrote only that he was moving on to "new challenges."

Griffin did not respond to requests for comment.

Gregory Starr, a deputy in the diplomatic security bureau, will take over as acting director, McCormack said.