HALF a century ago on July 16, the United States crossed the nuclear threshold by detonating the first atomic explosion - known as the Trinity Test - in the desolate New Mexico desert.
Over the intervening years, successive governments built history's most destructive military arsenal, globe-spanning systems to control it, missiles, ships, and planes to deliver it, and a vast industrial complex to sustain it.
Until now, the US government has never disclosed the full cost of these mammoth undertakings. But on July 11, a team of former government officials and independent experts released what they call the first comprehensive estimate of the huge sums poured into US nuclear arms programs.
Since the Manhattan Project, which produced the Trinity Test, American taxpayers have spent about $4 trillion creating a nuclear arsenal and related programs, according to the US Nuclear Weapons Cost Study Project.
The total represents between one-quarter and one-third of all US defense spending since 1945 - far more than ever officially acknowledged. The study, which draws on declassified documents, states that the price tag might actually be as much as $1 trillion higher.
"It's a minimal figure. It's a very conservative estimate," says Stephen Schwartz, a scholar at the Brookings Institution, a Washington think tank, and the director of the "Atomic Audit: What the US Nuclear Arsenal Really Cost."
"Nuclear weapons were sold to the American people as a less expensive, more effective alternative to massive conventional forces," Mr. Schwartz says. "But that was a specious argument because fielding the equivalent firepower with conventional forces was never a realistic possibility for both economic and political reasons."
In addition, he says, the nuclear-versus-conventional arms comparison focused solely on the weapons systems themselves and ignored the massive costs of the infrastructure and support systems required to maintain them.
The new study joins a growing number of reassessments of US cold war policies, which historians and other scholars are producing with the aid of volumes of newly declassified data. It comes as debate continues to swirl over how much to put into the nation's nuclear arsenal. The new GOP majority in Congress wants to boost spending for new nuclear weapons-related projects such as the B-2 bomber, even as the US and Russia reduce their atomic arsenals. Republicans argue defense spending has fallen periously low.
THE study notes most Americans believe that as disarmament moves ahead, the US has been able to cut spending on atomic arms. But the study states that while the government stopped building nuclear arms five years ago, halted underground tests in 1992, and cut the number of bombs and warheads from 21,000 to 14,000, it continues to spend $25 billion a year on nuclear weapons and weapons-related programs. And that amount, the study says, is destined to rise. "People don't understand that it is not like any sort of other enterprise. You just don't turn off the lights and walk away," Schwartz says.
Most of the $25 billion goes to maintaining the nuclear arms stockpile and keeping production plants in working order in case a decision is made to restart them, the study says. About $8 billion is spent to dispose of deactivated weapons and contain and clean up the radioactive waste left from the production of some 70,000 warheads and bombs since 1945.
Decommissioning more weapons as required by the US-Russia START I accord, environmental cleanups, and the long-term storage of unneeded nuclear materials and waste could eventually cost $200 billion and $500 billion per year, the study warns.
Among its other findings:
*The government devoted at least $12 billion to civil defense projects to protect the population from nuclear attack. But billions of dollars more were secretly spent on vast underground complexes from which civilian and military officials would run the government during a nuclear war.
*More than $75 billion was spent on weapons systems and programs that were based on "inadequately scrutinized assumptions" and later abandoned. These included nuclear-powered aircraft and rockets and former President Ronald Reagan's Strategic Defense Initiative, a plan for a nationwide defense against missile attack popularly known as "star wars."