Sens. John McCain, R-Ariz., and Barack Obama, D-Ill., say that Iran is developing nuclear weapons.

The U.S. intelligence community, however, thinks that Iran halted an effort to build a nuclear warhead in mid-2003, and the U.N. International Atomic Energy Agency, which is investigating the program, has found no evidence to date of an active Iranian nuclear-weapons project.

The candidates’ comments raise questions about how carefully the two have studied the public record on what’s become a major campaign issue and is one of the most difficult foreign-policy challenges likely to confront the next president.

The issue is also significant because the Bush administration inflated assessments of the Iraqi nuclear threat and the possibility that former dictator Saddam Hussein could pass nuclear weapons to terrorists as it sought to whip up public support for the March 2003 invasion of Iraq.

Iran has been expanding an industrial-scale uranium enrichment program in defiance of U.N. Security Council demands that it be suspended. Enrichment is the process that produces low-enriched uranium fuel for nuclear generating stations and highly enriched uranium for nuclear weapons.

Iran, whose known enrichment facilities are under IAEA monitoring, says it’s making low-enriched uranium reactor fuel and has no intention of developing weapons. Few experts, however, think that Iran has come clean about all its nuclear activities.

In a major speech Monday to a powerful Jewish American lobbying group, McCain asserted that Iran is actively developing nuclear weapons that threaten the security of Israel and could be passed to terrorist groups.

“Tehran’s pursuit of nuclear weapons poses an unacceptable risk, a danger we cannot allow,” he told the American Israel Public Affairs Committee.

Israel, however, is thought to have a significant nuclear arsenal of its own, and an Iranian nuclear attack on Israel would invite a devastating nuclear counterstrike.

In criticism aimed at Obama, McCain said, “The idea that they now seek nuclear weapons because we refused to engage in presidential-level talks is a serious misreading of history.”

McCain was referring to an interview Friday with Fox News in which Obama rebuked President Bush for rejecting direct negotiations with Iran on its nuclear program.

“Iran is stronger now than when George Bush took office,” Obama said. “And the fact that we have not talked to them means that they have been developing nuclear weapons.”

Neither campaign immediately responded to requests for comment on its candidate’s assertions.

The 16 agency-strong U.S. intelligence community said last November in an unclassified National Intelligence Estimate that it concluded with “high confidence” that Iran had halted an effort to develop a nuclear weapon in fall 2003.

A senior U.S. intelligence official, who requested anonymity because he wasn’t authorized to speak publicly, said that U.S. intelligence agencies stuck by the NIE’s judgment of “moderate confidence” that Iran hadn’t reactivated the alleged effort.

In Vienna, Austria, IAEA Director General Mohamed ElBaradei told his board of governors Monday that the agency is continuing to look into allegations that Iraq conducted secret studies related to developing a nuclear warhead for a missile.

The allegations are based on documents provided to the agency by the United States and other IAEA members that purport to show that Iran conducted the research until March 2004. Iran has dismissed the documents as forgeries.

ElBaradei said the IAEA couldn’t give the Iranian program a clean bill of health until Tehran had implemented “all the transparency measures required to clarify this cluster of allegations and questions.”

Democratic Sen. Hillary Clinton, who’s battling Obama for the Democratic presidential nomination, has been more nuanced in describing Iran’s nuclear program, telling MSNBC on April 21 that Iran “appears” to have a “continuing goal of obtaining nuclear weapons.”