In a letter sent to Sen. Jim Webb, D-Va., last week, Gates said he expects a preliminary response this week, The Virginian Pilot reported.

This month, Gates asked Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, for the review.

In a memo to Mullen, he asked: "Why have we come to rely on contractors to provide combat or combat-related security training? ... Are we comfortable with this practice?"

Blackwater, headquartered in Moyock, N.C., has become notorious since its security guards gunned down 17 Iraqi civilians in Baghdad, an attack that apparently started because some of the Blackwater guards felt threatened. The company, founded in the 1990s, began by operating training facilities for law enforcement agencies and the military.