WASHINGTON — The United States has now endured what by some measures is the longest period of war in its history, with more than 6,300 American troops killed and 46,000 wounded in Iraq and Afghanistan and the ultimate costs estimated at $3 trillion. Both wars lasted far longer than predicted. The outcomes seem disappointing and uncertain.

So why is there already a new whiff of gunpowder in the air?

Talk of war over Iran’s nuclear program has reached a strident pitch in recent weeks, as Israel has escalated threats of a possible strike, the oratory of American politicians has become more bellicose and Iran has responded for the most part defiantly. With Israel and Iran exchanging accusations of assassination plots, some analysts see a danger of blundering into a war that would inevitably involve the United States.

Echoes of the period leading up to the Iraq war in 2003 are unmistakable, igniting a familiar debate over whether journalists are overstating Iran’s progress toward a bomb. Yet there is one significant difference: by contrast with 2003, when the Bush administration portrayed Iraq as an imminent threat, Obama administration officials and intelligence professionals seem eager to calm the feverish language.

Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, said in a CNN interview on Sunday that the United States had advised Israel that a strike now would be “destabilizing,” adding that Iran had not yet decided whether to build a weapon. And American officials are weighing an Iranian offer to renew nuclear talks as a stream of threats from Tehran continued on Tuesday and international nuclear inspectors reported their mission to Iran had failed.