Citing last year's thwarted Iranian plot to kill the Saudi ambassador in the United States, "some Iranian officials - probably including Supreme Leader Ali Khamenei ... are now more willing to conduct an attack in the United States in response to real or perceived U.S. actions that threaten the regime," Clapper said.
Iran has the technical ability to build a nuclear weapon, Clapper said. But he, CIA Director David H. Petraeus, and others reasserted their stance that Iran is not building nuclear weapons, in subtle contrast to Israeli officials' statements that Iran could have nuclear capability within a year.
"There is dissension and debate in the political hierarchy of Iran" over whether to build a weapon, Clapper said. "There is not unanimity about this" as Iranian political officials weigh the regional prestige they believe they may gain by possessing a weapon against the cost of further international sanctions and the risk of retaliatory military action by Israel or the West.
Petraeus said the latest round of sanctions against the regime was beginning to bite, with a run on Iranian banks in recent weeks, but he conceded that the "clock is ticking" as Iran moves ahead enriching uranium to a grade that's below weapons-ready, but higher than normal for regular industrial use.
Defense Secretary Leon E. Panetta said in an interview aired this week that the Iranians could build a bomb quickly.
"If they decided to do it, it would probably take them about a year to be able to produce a bomb and then possibly another one to two years in order to put it on a deliverable vehicle of some sort in order to deliver that weapon," Panetta said Sunday on CBS's 60 Minutes.
Israeli Defense Minister Ehud Barak said last week that Iran was proceeding toward nuclear-weapons capability and that time was "urgently running out."
Petraeus said he met with the head of Israel's intelligence agency, Mossad, last week to discuss Israel's concerns.
While he said Israelis saw an Iranian nuclear weapon as "an existential threat to their country," he did not say whether Israel agreed with the U.S. assessment that Iran had not yet decided to make a nuclear weapon.
The Senate intelligence committee chairwoman, Dianne Feinstein, called 2012 "a critical year for convincing or preventing Iran from developing a nuclear weapon."
The threat of Iran lashing out as it ponders building nuclear arms is one of a mosaic of interconnected enemies facing the United States, including terrorists, criminals, and foreign powers who may try to strike via nuclear weapons or cyberspace, Clapper and the others said.
Al-Qaeda continues to be a major threat, though it is far weaker since Osama bin Laden's death at the hands of Navy SEALs in Pakistan last year. Petraeus pointed out that "four of the top 20 in a single week were captured or killed" last year, leaving the leadership struggling to replace itself. Clapper said the group likely would have to resort to "smaller, simpler attacks" as its ranks are thinned by continued pressure from U.S. drone strikes and special operations raids.
The intelligence chiefs predicted al-Qaeda's regional affiliates, such as Yemen's al-Qaeda in the Arabian Peninsula, will try to pick up the slack for the beleaguered core group in Pakistan.
Just below Iran and al-Qaeda on the list of threats is the possibility of proliferation of weapons of mass destruction, from chemical and biological to nuclear and radiological. The intelligence community does not believe states that possess them have supplied them to terror groups, but that remains a risk, Clapper said.
Air Strikes Kill 4 in Yemen
U.S. air strikes targeting leaders from Yemen's active al-Qaeda branch killed four suspected extremists, including a man suspected in the 2000 bombing of the USS Cole, officials said Tuesday.
Missiles struck a school and a car late Monday
in the southern Abyan province, Yemeni security and military officials said. Large swaths of the province have fallen under the influence of al-Qaeda as extremists exploit a security vacuum stemming from an uprising against President Ali Abdullah Saleh that began
U.S. officials consider
the Yemen branch of al-Qaeda to be one of the most dangerous. U.S. aircraft have targeted al-Qaeda leaders there before, notably killing Anwar al-Awlaki, a U.S. citizen, last year. The United States rarely comments on its air activity in Yemen.