The assessment said extended U.S. strikes could destroy Iran's most important nuclear facilities and damage its military forces but would only delay - not stop - the Islamic republic's pursuit of a nuclear bomb.
"You can't kill intellectual power," said retired Army Lt. Gen. Frank Kearney, who endorsed the report. He is a former deputy director at the National Counterterrorism Center and former deputy commander of U.S. Special Operations Command.
The report compiled by former government officials, national security experts and retired military officers is to be publicly released Thursday. It says achieving more than a temporary setback in Iran's nuclear program would require a military operation - including a land occupation - more taxing than the Iraq and Afghanistan wars combined.
An advance copy of the report was provided to The Associated Press."You can't kill intellectual power,"
The assessment emerges against the backdrop of escalating tensions between Israel and the U.S. over when a military strike on Iran might be required. The Israelis worry that Iran is moving more quickly toward a nuclear capability than the United States believes. The U.S. has not ruled out attacking but has sought to persuade Israel to give diplomacy more time.
Israel views a nuclear-armed Iran as a mortal threat, citing Iran's persistent calls for the destruction of the Jewish state, its development of missiles capable of striking Israel and Iranian support for Arab militant groups.
Tehran insists its nuclear program is for peaceful purposes only.
An oft-stated argument against striking Iran is that it would add to a perception of the U.S. as anti-Muslim - a perception linked to the U.S.-led invasions of Iraq and Afghanistan and hardened by Internet-based video excerpts of an anti-Muslim film that may have fueled Tuesday's deadly attack on a U.S. diplomatic office in Libya. More