Those plans may grow more ambitious, senior administration officials say, as the White House seeks new ways to counter North Korea, push back against Iran and deal with significant nuclear modernization in both Russia and China. The authors of the Nuclear Posture Review were told they could consider the building of new types of nuclear weapons, even some now prohibited by treaty.
Any changes could drive up the estimated cost of rebuilding the nation’s arsenal, and the figures released Tuesday did not account for inflation, which independent experts say would drive the total figure to more than $1.6 trillion.
The overall direction of the buildup may also end the discussion, driven by Mr. Obama during much of his term, about how to reduce the role of nuclear weapons in American offensive and defensive planning. In the end Mr. Obama walked back from his vision, deciding against eliminating one leg of the “triad” — made up of weapons carried aboard ground-based missiles, submarines and bombers — and he rejected advice from some of his top nuclear strategists about how to bring the total number of deployed American weapons below 1,000, even if President Vladimir V. Putin was not willing to make similar cuts.
Critics of the American arsenal, who grew increasingly frustrated with Mr. Obama, have urged Mr. Trump to pare back, for reasons of budget if not strategy.
Two former senior military officials, William J. Perry, who served as secretary of defense, and Gen. James E. Cartwright, who served as vice chairman of the Joint Chiefs of Staff, described the congressional report as “a wake up call” in a letter Tuesday to Mr. Trump. The report demonstrated that current plans to rebuild the nuclear arsenal “are unsustainable and must be rethought,” they wrote.
The report, about 70 pages long, details nine cost-cutting options for Congress that run from relatively minor to more extensive.
One option, for example, examined the savings if the administration decided to forego a new generation of nuclear cruise missiles — low-flying weapons with stubby wings that, when dropped from a bomber, hug the ground to avoid enemy radars and air defenses.
The weapon was endorsed by Mr. Obama, though it has been criticized by other Democratic nuclear experts, like William Perry, as destabilizing. In any event, its elimination would save only about $30 billion — about 2.5 percent of the total nuclear expenditures.
Another option called for deploying fewer submarines and intercontinental ballistic missiles than currently planned. Over three decades, that would save $85 billion. Scrapping the aging land-based missiles altogether would result in the largest savings, $175 billion.
“It explodes the myth that the plan’s proponents have been trying to foist on us — that it’s all of the above or nothing,” said Daryl G. Kimball, executive director of the Arms Control Association, a private group in Washington. “The reality is that there’re a number practical options to save tens of billions of dollars while still maintaining a robust nuclear force.”
The $1.2 trillion figure over three decades compares to annual expenditures for Medicare of about $650 billion and for Medicaid of about $550 billion.
“The stark reality underlined by C.B.O. is that unless the U.S. government finds a pot of gold at the end of the rainbow, the nuclear weapons spending plan inherited by the Trump administration will pose a crushing affordability problem,” said Kingston Reif, director for disarmament and threat reduction policy at the Arms Control Association.
While Mr. Trump likes to take credit for the nuclear weapons push, the costly makeover actually began with Mr. Obama, despite his repeated calls for “a world without nuclear weapons.” Mr. Obama argued that by making nuclear weapons safer and more reliable, their numbers could eventually be reduced, setting the world on a path to their elimination. Some of Mr. Obama’s aides, thinking that Hillary Clinton would win the presidential election, expected deep cuts in the $1 trillion plan.
Mr. Trump inherited the costly makeover, and his first budget proposed to move fully ahead with the Obama administration approach — and then some. In an August speech, he boasted that his administration was spending “vast amounts” on overhauling the nuclear arsenal.
Administration critics and arms control advocates say the Congressional Budget Office report reveals how extraordinarily difficult it will become in future years to maintain the nuclear weapons plan and the administration’s promises as the costs of the rebuilding program begin to soar.
“Many elements of Trump’s nuclear spending spree are excessive and dangerous,” said Tom Z. Collina, policy director at Ploughshares Fund. “We would be safer and richer without them.”
Mr. Perry, the former defense secretary, argued last year in a New York Times Op-Ed article that eliminating the ground-based missiles would improve global security. “These missiles are some of the most dangerous weapons in the world,” he wrote. “They could even trigger an accidental nuclear war” because their vulnerability to pre-emptive strikes would, in a time of crisis, give the president an incentive to launch them.
Critics see the nation’s launch-on-warning policy as greatly increasing the risk of accidental war. In the past, they note, false alerts have repeatedly brought the world to the brink of thermonuclear disaster.
“We should consider all aspects of our nuclear posture, and our conventional forces’ needs,” Mr. Perry and General Cartwright wrote to Mr. Trump, “before rushing headlong into these expensive and contentious development programs.”