Under the accord, the two sides agreed to reduce their numbers of deployed nuclear warheads to no more than 1,550 within seven years.

The United States, based on the Bush administration guidance, had been prepared to go below the 1,550 figure, the former administration official said, but the Russians resisted.

Even with the higher number, the administration had difficulty winning ratification in the Senate.

Early on, Obama and his aides had been surprised by the poor state of aging U.S. nuclear weapons facilities that manufacture plutonium and uranium components for warheads.

He told his Prague audience he was committed to maintaining a safe, secure and effective U.S. nuclear arsenal as long as the weapons existed. And he committed to investing a substantial amount of money in upgrading the nuclear weapons complex.

During Senate debate over New START, Republican Sen. Jon Kyl wrested a pledge for another $4.1 billion for nuclear modernization, drawing criticism from arms control groups that questioned why Washington would spend more on the nuclear complex when it aimed to eliminate the weapons.

Obama has pledged “as much as $214 billion to modernize that complex as well as the delivery systems, you know the submarines, the bombers and what have you,” said Hans Kristensen, director of the nuclear information project at the Federation of American Scientists.

“It’s somewhat of a schizophrenic nuclear policy.”

Six weeks after the treaty’s passage, Obama wrote to the Senate promising to modernize the triad of nuclear delivery systems and “to accelerate to the extent possible” work on the plutonium and uranium production facilities at Los Alamos, New Mexico, and Oak Ridge, Tennessee.

Months later, amid rising Republican pressure to curb government spending, he essentially reneged on the deal, offering budget plans that funded the uranium facility work while pushing the plutonium plant beyond a 10-year planning horizon.