A new census of the American nuclear arsenal shows that the Obama administration last year dismantled its smallest number of warheads since taking office.

The new figures, released by the Pentagon, also highlight a trend — that the current administration has reduced the nuclear stockpile less than any other post-Cold War presidency.

On Thursday, the Federation of American Scientists, a private group in Washington that strongly supports arms control, issued an analysis of the new figures on its Strategic Security blog. The annual Pentagon release did not appear to be linked to President Obama’s visit Friday to Hiroshima, Japan, which was destroyed by an American atomic bomb almost 71 years ago.

Still, the new figures and private analysis underscored the striking gap between Mr. Obama’s soaring vision of a world without nuclear arms, which he laid out during the first months of his presidency, and the tough geopolitical and bureaucratic realities of actually getting rid of those weapons.