Nuclear weapons will continue to play a key role in U.S. security policy for many decades. Yet the Department of Defense (DOD) and the National Nuclear Security Administration (NNSA), the Department of Energy (DOE) agency in charge of the nuclear weapons program, have raised concerns that maintaining current weapons, which date from the Cold War, will become increasingly difficult. At issue for Congress is how best to maintain the nuclear stockpile so that it will retain, for many decades, capabilities that political and military leaders deem necessary. There are three main options: (1) extend the service lives of current warheads without nuclear testing; (2) develop, build, and deploy a new generation of warheads without testing to replace the current stockpile; or (3) resume nuclear testing, which the United States suspended in 1992, as a tool to help maintain existing warheads or develop new ones. This report focuses on the first two options. It compares how they respond to congressional goals, presenting pros, cons, uncertainties, costs, and potential risks and benefits, then discusses issues for Congress. Regarding the third option, the United States has not conducted a nuclear test since 1992, yet has assessed for the past 12 years that current warheads are safe and reliable. On the other hand, some would resume testing on grounds that that is the only way to be sure that U.S. nuclear weapons remain safe and reliable, to validate tools for maintaining weapons without testing, and to develop new weapons if needed. However, the Administration and many in Congress prefer not to resume nuclear testing, so this report does not consider it as a separate option, but discusses it at various points because testing would provide additional data to help maintain or develop nuclear weapons. This report does not consider a fourth option, abolition of U.S. nuclear weapons, as it has garnered no support in Congress or the Administration. Almost all warheads in the current stockpile were built in the 1970s and 1980s. They require ongoing surveillance and maintenance because their components deteriorate. In the wake of the nuclear test moratorium that the United States has observed since 1992, Congress instituted the Stockpile Stewardship Program (SSP) in 1993 "to ensure the preservation of the core intellectual and technical competencies of the United States in nuclear weapons." SSP has provided the technical basis for advancing the relevant science in an effort to maintain confidence in U.S. warheads without nuclear testing. NNSA requests $6,511.3 million for SSP, under the heading "Weapons Activities," for FY2008. Part of SSP is the Life Extension Program (LEP), which seeks to maintain warheads by replacing certain components, as needed, with newly-fabricated ones that stay as close as possible to the originals; other components may be modified. For details on congressional action on FY2008 authorization and appropriations bills, see CRS Report RL32929, The Reliable Replacement Warhead Program: Background and Current Developments , by Jonathan Medalia , which provides background and tracks legislation and developments. NNSA is concerned that it will become increasingly difficult to maintain high confidence in current warheads for the long term with LEP. Reflecting this concern, Congress initiated the Reliable Replacement Warhead (RRW) program in the FY2005 Consolidated Appropriations Act ( P.L. 108-447 ) "to improve the reliability, longevity, and certifiability of existing weapons and their components." NNSA executes the RRW program in cooperation with DOD, the "customer" for nuclear weapons, through the Nuclear Weapons Council, a joint DOD-NNSA organization that oversees and coordinates nuclear weapon activities. When DOD needs a new warhead, or when NNSA must modify a warhead, the council establishes a warhead Project Officers Group (POG) to develop draft "military characteristics" that the warhead must meet, such as explosive yield. The RRW POG has representatives from key stakeholders: Office of the Secretary of Defense, NNSA, U.S. Strategic Command, Navy, Air Force, and design teams. It spelled out military characteristics for RRW and established RRW program priorities that the council has vetted. Safety is the first priority; security/use control is the second. Others—certifiability, cost, longevity, manufacturability, reliability, survivability in nuclear environments, and yield—are not rank-ordered. NNSA must also meet policy goals in designing or maintaining warheads. Congress, mainly through FY2006 legislation and committee reports, spelled out at least 20 goals for RRW in the following categories: reduce the need for nuclear testing; improve safety and use control; design for manufacturing and maintenance; fulfill current mission requirements but not new ones; facilitate upgrading the nuclear weapons complex (the "Complex"; see Appendix A ); and reduce the cost of the stockpile and Complex. RRW designs seek to meet all these goals. The Nuclear Weapons Council started a competition between a New Mexico (NM) design team composed of Los Alamos National Laboratory (LANL) (NM) and Sandia National Laboratories' NM site, and a California (CA) team of Lawrence Livermore National Laboratory (LLNL) (CA) and Sandia's CA site. Both teams created preliminary warhead designs between October 2005 and March 2006, then did further detailed design work. According to a December 2006, statement, the Nuclear Weapons Council determined that RRW is a feasible strategy for sustaining U.S. nuclear weapons without testing. It selected the California design in March 2007 as the first RRW, or RRW-1. This warhead is now called "WR1." Nuclear weapons development proceeds in "phases" that have been defined for many years, from Phase 1 (concept assessment) to Phase 7 (retirement). For FY2008, NNSA requests funds mainly for Phase 2A (design definition and cost study), with some funds for Phase 3 (development engineering). As of July 2007, the Navy-led RRW POG is conducting a Phase 2A, design definition and cost study. The Lawrence Livermore, Los Alamos, and Sandia National Laboratories are working within the POG study to refine the design, review tradeoff options, plan the potential development program, and estimate costs of the California design. The choice between LEP, RRW, or some combination is important because it will set the course for U.S. nuclear weapons for decades to come, and each year it is up to Congress to decide whether to fund these programs as requested, or modify or cancel them. A crucial decision is whether to move RRW to Phase 3 from the current Phase 2A. While the Nuclear Weapons Council had envisioned completion of Phase 2A by the end of December 2007, it appears unlikely that Congress will make a decision on Phase 3 in the FY2008 budget cycle, as the defense authorization bills reported by the House and Senate Armed Services Committees ( H.R. 1585 and S. 1547 , respectively) and the energy and water appropriations bill reported by the Senate Appropriations Committee ( S. 1751 ) recommended holding RRW in Phase 2A in FY2008. Further, the energy and water appropriations bill as passed by the House ( H.R. 2641 ) provided no funds for RRW. There are many RRW issues to resolve. Cost is important to any decision to proceed with RRW, yet long-term cost projections are notoriously unreliable. There are technical uncertainties, such as whether the winning RRW design can be turned into a functioning warhead. The future Complex has yet to be determined, along with how it might differ depending on whether the United States pursues LEP or RRW and how it would handle a transition to an all-RRW stockpile. Stockpile numbers decades out are unknowable, yet a Complex would spend money unnecessarily if sized too large and could not support requirements if sized too small. A commenter noted that while claims are made that RRW is cheaper, safer, more reliable, etc., than LEP, or vice versa, in many cases "no numbers exist to substantiate the claim. The proponents of either approach, in many cases, while implying a measurable effect are really saying 'believe me.'" Beyond RRW issues are broader issues of strategic policy. Accordingly, many in Congress want NNSA to use FY2008 to perform further Phase 2A work, and others to study broader issues. For example, the report on H.R. 2641 stated: "it is premature to continue design activities for a new nuclear warhead until a revised U.S. nuclear weapons strategy is developed that describes the long term nuclear stockpile requirements and demonstrates how a new nuclear warhead is necessary to address specific U.S. national security requirements and nuclear nonproliferation commitments." The House Armed Services Committee called for a congressional commission on U.S. strategic posture in its FY2008 national defense authorization bill, H.R. 1585 . It said, "The committee believes clear policy objectives should be established before Congress commits to ambitious new programs." The commission's report would be due by December 1, 2008. Section 1061 of S. 1547 , the Senate Armed Services Committee's defense authorization bill, called for a revised nuclear posture review that, among other things, would "includ[e] any plans for replacing or modifying warheads." The committee's report states that the report would be due to Congress in December 2009. Consistent with that language, Congress might decide to hold RRW in Phase 2A until the next President reviewed U.S. nuclear policy and the possible role of RRW in it. The earliest that a request to move RRW to Phase 3 could be made as part of the regular budget process would then be the budget submitted in February 2010 (i.e., the FY2011 budget). In that case, Phase 3 work could not begin before October 2010.