The nation’s top military officer said Sunday that Iran has enough nuclear material to make a bomb, but Defense Secretary Robert M. Gates said Tehran was not close to building a weapon.

Adm. Michael G. Mullen, chairman of the Joint Chiefs of Staff, told CNN’s “State of the Union” program that he believed Iran had enough fissile material for a nuclear weapon.

“We think they do, quite frankly,” Mullen said.

A recent report by the International Atomic Energy 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. It takes about a ton of enriched uranium to make a nuclear bomb.

Although a November 2007 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.

Mullen said Sunday that the U.S. remains strongly opposed to a nuclear-armed Iran.

“And 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 Iran from making a bomb was a top U.S. priority. But he said a diplomatic solution remains 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.”

Although Iran says the enrichment program is for a civilian nuclear reactor, the U.S. and other governments believe the Iranians intend to use the uranium for a weapon.

Gates said the question for the U.S. was whether the U.N. would be willing to increase the sanctions imposed on Iran. 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 engage Iran. With lower oil prices reducing Iran’s leverage, the prospects for increasing pressure on the nation have improved, Gates said.

“There has been a continuing focus on how do you get the Iranians to walk away from a nuclear program,” Gates said.

Iran’s pursuit of nuclear weapons and missile technology is a critical issue for the U.S. and NATO. Under the Bush administration, the U.S. pushed for a 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 if the new administration will slow down or cut back the program

On “Fox News Sunday,” Mullen said he expected the Obama administration to conduct a review of missile defense. Such a policy evaluation would influence how much funding the program gets in the future.

Although many Democrats, including some now in the Obama administration, have been skeptical of the efficacy of missile defense, the system could face a potential real-world test in the days to come.

North Korea has said it plans a test of its longest-range missile. Key military leaders have suggested the U.S. could shoot down that missile. Striking the North Korean missile would lay aside some of the doubts about the missile defense program, but could 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 and continued under the Obama administration. In the NBC interview, Gates was asked to compare the two 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.

Iran has the materials to make a nuclear bomb, top U.S. official says