WASHINGTON — The National Nuclear Security Administration is underestimating how much funding it needs to update and maintain America's nuclear warheads, a government watchdog has concluded.

A new Government Accountability Office report on the NNSA, a quasi-independent branch of the Department of Energy that manages the nuclear stockpile, warns that the agency has five major modernization programs that will be underfunded in the coming years — which in turn could lead to program delays.

"This misalignment indicates that estimated budgets may not be sufficient to fully execute program plans and that NNSA may need to increase budget estimates for those programs in the future," GAO investigators concluded.

NNSA's most recent budget request was for $49.4 billion for fiscal years 2017 through 2021, with about $9.2 billion for 2017. The agency has estimated that between 2017 and 2041, modernization costs will sit at just over $300 billion.

The five programs the GAO raised concerns about are the W76-1 Life Extension Program, which will extend the life on the Navy’s Trident II D5 submarine-launched ballistic missile; the B61-12 Life Extension Program, which seeks to combine a number of B61 bomb variants into a more modernized nuclear gravity bomb; the W80-4 Life Extension Program, whose goal is to provide a warhead for a future long-range standoff missile that will replace the Air Force’s current air-launched cruise missile; the IW-1 Life Extension Program, which is meant to create an interoperable warhead for various systems; and the W88 Alteration 370, which will replace the arming, fuzing and firing subsystem for the W88 warhead for the Trident II.

The budget differential is so large that in some cases, the low end of NNSA’s cost-range estimates exceeds the estimates in the budget materials. For instance, the GAO found that the W80-4 program’s low-range cost estimate for FY2017 exceeds the budget estimate by about $26.9 million.

"In addition, the budget estimates for some modernization programs for fiscal years 2018 through 2021 are more than $5 billion below the funding levels NNSA has identified needing. If these needs are not met, NNSA may have to defer certain modernization work," the GAO report states. "NNSA’s fiscal year 2017 plan concludes that the modernization program is generally affordable in the years beyond the [Future-Years Nuclear Security Program], but this conclusion is optimistic, and the NNSA plan does not assess options to align future modernization plans and budgets with or without out-year funding increases."

The report’s release coincides with the start of the Nuclear Posture Review, a major look at how America’s military arsenal is designed, modernized and maintained. That review is expected to be completed before the end of the year and will help guide the fiscal 2019 budget plan.

The GAO’s report drew attention from the nonproliferation community, with Kingston Reif of the Arms Control Association calling it "devastating" and a sign of the "coming fiscal train wreck facing NNSA's weapons program."

"The report makes it clear that NNSA's current plan is unrealistic and probably unexecutable and that the agency has no real plan to address the mismatch between its plans and budgets other than to kick the can and hope for more money," Reif said. "This is a recipe for further cost overruns, schedule delays and mindless cuts to higher-priority NNSA programs, namely nuclear security and nonproliferation."

In a response summarized by the GAO report, the NNSA did not address each of the watchdog’s concerns but more generally pointed out that estimating funding for programs into the 2030s and beyond is complicated and, by nature, reflect broad estimates rather than hard programing figures. Complicating the issue, the GAO acknowledged, is the question of sequestration and what the budget caps may look like in the future.

One area the GAO says the agency is doing a good job? Trying to tackle its backlog of deferred maintenance, including the creation of a "Top 10" list of the biggest problem sites and trying to use FY2017 funding to address those concerns. Frank Klotz, the NNSA head, has also been vocal about his maintenance concerns in public statements, as well as during congressional testimony.