Defense Secretary Panetta says Iran isn't building nuclear bomb, but laying groundwork for one.

The Associated Press - Defense Secretary Leon Panetta says Iran is laying the groundwork for making nuclear weapons someday, but is not yet building a bomb and called for continued diplomatic and economic pressure to persuade Tehran not to take that step.

As he has previously, Panetta cautioned against a unilateral strike by Israel against Iran's nuclear facilities, saying the action could trigger Iranian retaliation against U.S. forces in the region.

"We have common cause here" with Israel, he said. "And the better approach is for us to work together."

Panetta's remarks on CBS' Face the Nation, which were taped Friday and aired Sunday, reflect the long-held view of the Obama administration that Iran is not yet committed to building a nuclear arsenal, only to creating the industrial and scientific capacity to allow one if its leaders to decide to take that final step.

The comments suggest the White House's assessment of Iran's nuclear strategy has not changed in recent months, despite warnings from advocates of military action that time is running out to prevent Tehran from becoming a nuclear-armed state.

Iran says its nuclear program is only for energy and medical research, and refuses to halt uranium enrichment

Several Republican candidates have called for a tougher line against Iran, saying they believe it is committed to building the bomb.

"If we re-elect Barack Obama, Iran will have a nuclear weapon," said Mitt Romney. "And if you elect Mitt Romney, Iran will not have a nuclear weapon."

Rick Santorum has said that the U.S. should plan a military strike against Iran's nuclear facilities and "say to them that if you do not open up those facilities and close them down, we will close them down for you."

Iran has opened two dozen of its facilities to international inspectors, but has refused in defiance of the U.N. Security Council to suspend its uranium enrichment.

In a talk at a Brookings Institution forum in December, Panetta said an attack on Iran's nuclear facilities would "at best" delay Iran's nuclear program by one or two years. Among the unintended consequences, he said, would be an increase in international support for Iran and the likelihood of Iranian retaliation against U.S. forces and bases in the Mideast.

Panetta did not discuss the issue directly on Sunday's "Face the Nation." But Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey, appearing with the defense secretary, said that he wanted the Iranians to believe that a U.S. military strike could wipe out their nuclear program.

"I absolutely want them to believe that's the case," he said.

Panetta did not rule out launching a pre-emptive strike.

"But the responsible thing to do right now is to keep putting diplomatic and economic pressure on them to force them to do the right thing," he said. "And to make sure that they do not make the decision to proceed with the development of a nuclear weapon."

Panetta said if Iran started developing a weapon, the U.S. would act.

"I think they need to know that - that if they take that step - that they're going to get stopped," Panetta said.

Dempsey also said that Iran has the military power to block the Strait of Hormuz "for a period of time" if it decides to do so, but that the U.S. would take action to reopen the waterway. "We can defeat that," he said.