The United States and the Soviet Union, along with a number of other nations, are currently negotiating two major arms control treaties that would limit various types of military forces. At the same time, political changes are reducing general military tensions. In response, the Congress is beginning a debate over major reductions in U.S. military forces that is likely to last for several years. To provide information for this debate, this Congressional Budget Office (CBO) paper analyzes the costs and military effects of a wide range of possible changes in U.S. forces. The paper documents analyses presented in testimony requested by the Subcommittee on Military Personnel and Compensation of the House Armed Services Committee. Portions of the analysis dealing with the costs and effects of the Strategic Arms Reduction Talks (START) treaty and the Conventional Forces in Europe (CFE) treaty were performed at the request of the Ranking Minority Member of the Senate Budget Committee. Further information on these analyses is available in the CBO Special Study, "Budgetary and Military Effects of a Treaty Limiting Conventional Forces in Europe," January 1990, and the CBO Staff Memorandum, "Budgetary and Military Effects of the Strategic Arms Reduction Talks (START) Treaty," February 1990. The analysis of reserve transfers is being done at the request of the Chairman of the Senate Budget Committee. Unless the treaty negotiations fail or the political changes are reversed, these events will eventually make the world a safer place in which to live and reduce the requirement for U.S. military capability. This CBO Paper examines five alternative force "structures" (that is, numbers and types of forces) that reflect widely differing judgments about the desirable amount of reduction. It assesses the cost and effects of each alternative on manpower as well as its effects on military capability.