Army preparing for steep drawdown, losing patience with congress.

• Position: Form the National Defense Blog

The Army is drawing up plans for how it would operate with nearly 100,000 fewer troops. The analysis will identify specific missions and duties the Army would no longer be able to do at that smaller size.

"If we go below 450,000, we have to redo the strategy," said Gen. John F. Campbell, the Army's 34th vice chief of staff who is taking over as the new commander of U.S. command of the war in Afghanistan.

The Army already is on a path to shrink from 513,000 active-duty soldiers to 490,000 by 2015, and 450,000 by 2017. But unless Congress repeals the spending limits set by law through 2021, the Army would have to downsize further, to 420,000, by 2019.

Army Chief of Staff Gen. Ray Odierno directed a "total Army analysis" of how the service would cope with the tighter budget squeeze. The...