The nation's top military officer said Sunday that Iran had enough nuclear material to make a bomb, but Defense Secretary Robert M. Gates said Tehran was not close to building such a weapon.
"We think they do, quite frankly," said Mullen, who reiterated the dangers of a nuclear-armed Iran.
"Iran having nuclear weapons, I've believed for a long time, is a very, very bad outcome -- for the region and for the world," Mullen said.
Gates, speaking on NBC's "Meet the Press," agreed that deterring Tehran from making a bomb was a top U.S. priority. But he said a diplomatic solution remained possible.
"They are not close to a stockpile; they are not close to a weapon at this point," Gates said. "So there is some time." Mullen commented in response to a question about a recent report by the U.N.'s nuclear monitoring body, the International Atomic Energy Agency. The agency found that Iran had built up its supplies of enriched uranium to slightly more than a ton, about 33% more than Tehran had previously stated it had stockpiled. Some experts say it takes about a ton of enriched uranium to make a nuclear bomb.
Although a November 2007 U.S. National Intelligence Estimate found that Iran had stopped developing a nuclear weapon, senior U.S. officials now discount that conclusion. Since taking office, President Obama and other top administration officials have said repeatedly that Tehran is pursuing nuclear weapons.
Iran says the enrichment program is meant solely for civilian energy purposes.
Gates said it was unclear whether the United Nations would be willing to increase sanctions on Iran to try to persuade it to quell its nuclear activities. But he also noted that the U.S. would show Tehran an "open door," an apparent allusion to Obama's statements during the presidential campaign that he would be willing to engage Iran in talks. With lower oil prices reducing Iran's leverage, the prospects for increasing pressure on the nation have improved, Gates said.
Iran's pursuit of nuclear and missile technology is a crucial issue for the U.S., Israel and the North Atlantic Treaty Organization. Under the Bush administration, the U.S. pushed for an Eastern European missile defense system to protect against Iranian rockets. In the past, Obama and some of his key advisors have been skeptical of missile defense; military officials are wondering whether the new administration will slow down or cut back the program.
On "Fox News Sunday," Mullen said he expected the administration to conduct a review of missile defense. Such an evaluation would influence how much funding the program gets.
In coming days, the U.S. missile defense system potentially could face a real-world test. North Korea has said it plans a trial of its longest-range missile, believed to be capable of reaching Alaska.
Key military leaders have suggested the U.S. could shoot down that missile. Striking a North Korean missile would lay aside some of the doubts about the missile defense program, but could also prove controversial. North Korea has said the test is part of preparations to send a satellite into orbit.
"We have made no decisions; the president has made no decisions," Mullen said. "I have made no recommendations as to what the North Koreans might do. I would hope that the North Koreans would not be provocative, and we are keeping a very close eye on what they do."
Gates and Mullen are the two most prominent officials to have served under President Bush who are part of the Obama administration. In the NBC interview, Gates was asked to compare the presidents' styles.
"It is really hard to say," Gates said. "I think probably President Obama is somewhat more analytical. He makes sure he hears from everybody in the room on an issue."
Gates said if an advisor does not speak up, Obama calls on him or her.
"President Bush was interested in hearing different points of view," Gates said. "But he didn't go out of his way to make sure everybody spoke."
Gates and Mullen appeared on the news shows primarily to talk about the Obama administration's Iraq drawdown plan, which was announced Friday.
Under the plan, the U.S. will withdraw about 100,000 troops by Aug. 31, 2010, leaving a transitional force of up to 50,000 troops for 16 more months.
Mullen contended that the success of military actions since the Bush administration's troop buildup strategy had allowed the military to embrace Obama's plans.
"The conditions are much more positive than they were two years ago, and the conditions are set for the government of Iraq to take over their own country," Mullen said.
The large size of that residual force has upset some Democratic lawmakers, including House Speaker Nancy Pelosi.
Gates said that having tens of thousands of troops would be a hedge against pulling forces out more quickly than top commanders had wanted.
"If the commanders had complete say, they would have preferred that the combat mission not end until the end of 2010," Gates said. "So having a somewhat larger residual or transition force mitigates the risk of having the combat units go out sooner."
Gates emphasized that, with 18 months to go, the U.S. had time to help the Iraqi government solve security problems in Mosul and other parts of the country.
Obama could alter the timeline in the event of a flare-up of violence or another contingency, but Gates said he doubted the plan would change.