Washington ? There was no hint of it in the bland resignation letter, but it was Blackwater USA that did in the State Department’s security chief.

The storm over last month’s deadly Blackwater shooting in Baghdad and the fury over the department’s security practices in Iraq claimed their first Washington casualty on Wednesday, forcing the assistant secretary of state for the Bureau of Diplomatic Security to step down.

Richard Griffin’s resignation came amid growing questions about the use of private contractors and was not voluntary, according to officials familiar with the circumstances of his departure. He had been under withering criticism for the agency’s lax oversight of private guards who protect U.S. diplomats in Iraq, notably those from Blackwater accused of killing 17 Iraqi civilians on Sept. 16.

Griffin made no mention of the furor in his letter to President Bush and Secretary of State Condoleezza Rice.

His departure followed by just a day the release of a report commissioned by Rice that found serious lapses in the department’s oversight of private guards, who are employed by and report to the bureau where where Griffin had worked.

Rice accepted the resignation, which is effective Nov. 1. State Department spokesman Sean McCormack said Griffin will be replaced on an acting basis by one of his deputies, Gregory Starr.

“I just want to thank him for his exemplary service to the country,” Rice told reporters before meeting with Iraqi deputy Prime Minister Barham Salih.

Griffin, an ambassador-rank official who was previously deputy director of the U.S. Secret Service and inspector general for the Department of Veterans Affairs, had been in his current job since June 2005. He served 36 years in the U.S. government, according to his official biography.

The change comes at a critical time in the debate over the State Department’s reliance on private security guards and the rules under which they operate after the Sept. 16 shooting in which Blackwater personnel are accused of killing 17 Iraqi civilians.

Earlier Wednesday in Baghdad, the Iraqi cabinet upheld the findings of an official investigation of the incident that found the guards opened fire without provocation. Blackwater disputes this, saying the U.S. Embassy convoy it was protecting was attacked first.

The Iraqi cabinet also renewed calls for Blackwater’s expulsion from Iraq and set up a committee to look into repealing a 2004 directive that gives private contractors virtual immunity from prosecution.