The U.S. plan for modernizing the nation’s nuclear arsenal is so expensive that it cannot be implemented, the authors of a new study contend.

"It's just not real," Jeffrey Lewis, one of the report's co-authors, said in reference to the current U.S. modernization blueprint. "It's inconceivable to me that we will execute anything like the plan that they say they're going to do."

The analysis, released on Tuesday by the James Martin Center for Nonproliferation Studies, says the strategy to update the U.S. triad of nuclear-armed bomber aircraft, submarines and ground-based missiles would cost $1 trillion over the next 30 years, even under conservative assumptions.

The estimate relies largely on official government figures, the authors say, and does not include costs associated missile defense, nonproliferation efforts and related intelligence programs.

Instead, it includes only the cost of maintaining the current U.S. nuclear arsenal, buying replacement systems and upgrading bombs and warheads, as called for by the current plan. Major cost drivers of the $1 trillion plan include a new Long-Range Strike bomber, which the report projects will cost $55-100 billion, and Ohio-class replacement submarines, which the study says could cost $77-102 billion.

Among the more controversial items on the modernization agenda are plans to upgrade B-61 gravity bombs stationed in Europe, create a new Long-Range Standoff Cruise missile, and develop a series of new, interoperable warheads capable of replacing multiple weapons now in the U.S. nuclear arsenal.

Given current budget constraints, implementing all of these plans simultaneously is so unrealistic that attempting it would likely backfire and cause major projects to be canceled midstream, said Lewis, speaking during the study's Tuesday public roll-out. Doing nothing to inject realism into the plans in the near term could ultimately leave aging weapons without replacements, Lewis forecasted.

"I do not support unilateral nuclear disarmament, but if I did, [I'd recommend that we] just keep doing exactly what we're doing," Lewis said. "We might really end up with this tiny little denuded force that was developed with no particular strategic thought in mind.

"The example I think of is -- we're talking about spending $10-12 billion on the B-61 [bomb] at this moment, at the very time the Air Force is making all kinds of signals that it will not make nuclear-capable the F-35” Joint Strike Fighter or nuclear-certify from the outset the planned new Long-Range Strike bomber, Lewis added. "So, we'll spend $12 billion on a bomb that won't have an airplane to drop it."

Lewis and co-author Jon Wolfsthal, both CNS issue experts, said the purpose of the study was to encourage policymakers to consider the full cost of the current plan, so that it can be ultimately amended based on strategic goals that fit within realistic financial constraints.

The report's sole recommendation is that Congress require the White House Office of Management and Budget -- along with the Energy and Defense departments -- "to annually produce an integrated nuclear deterrence budget" that projects the full cost of each system in the U.S. nuclear arsenal over its operational lifetime.

The nonpartisan Government Accountability Office has issued findings that support the idea that Congress and the executive branch do not fully understand the lifetime costs of the current modernization plan, according to the CNS report.

A 2005 GAO assessment demonstrated that "the United States does not know with any accuracy how much it spends annually on its nuclear deterrent, or how much it will cost to replace the current triad," the CNS report notes.

"The longest-range estimates for the nuclear mission produced by the administration were in 2010 and contained about $214 billion in spending over the fiscal 2011-20 period, but the report omitted significant costs, and the estimate period ends just before the substantial procurement bills come due," the new study contends.

Congressional sources have suggested that budget realities might be causing the Obama administration to back away from certain aspects of the modernization plan, potentially to include concepts for developing interoperable warheads.

Officially, however, the White House has stood by the plan, objecting to a provision in the fiscal 2014 defense authorization law that requires a study on whether it would be cheaper to simply refurbish existing warheads.

Other issues -- such as whether ground-based ballistic missiles are as important in the post-Cold War era as harder-to-detect missile-carrying submarines -- should also be discussed, Lewis and Wolfsthal suggested.

They acknowledged, however, that eliminating ICBMs entirely would be politically difficult, given the staunch support they receive from lawmakers representing the Western states where they are based.

"The problem," according to Lewis, "is that at this particular moment there is a lack of courage on the part of the White House and excessive partisanship in Congress. The president stands up in Berlin and talks about negotiating an additional reduction with the Russians to go down to 1,000 deployed warheads and he's immediately condemned for supporting what amounts to unilateral disarmament.

"What strikes me as one of the central findings of this report is we will be lucky to be at 1,000 warheads by 2030," Lewis contended. "What we're trying to do is to get people to look realistically at what the levels of budgetary authority are going to be and then have this conversation."