The secret missions have been going on at least since last summer with the goal of identifying target information for three dozen or more suspected sites.

According to one government consultant with close ties to the Pentagon, "The civilians in the Pentagon want to go into Iran and destroy as much of the military infrastructure as possible."

One former high-level intelligence official says "this is a war against terrorism, and Iraq is just one campaign. The Bush administration is looking at this as a huge war zone. Next, we're going to have the Iranian campaign."

The White House said Iran is a concern and a threat that needs to be taken seriously.

"We obviously have a concern about Iran. The whole world has a concern about Iran," Dan Bartlett, a top aide to President Bush, told CNN's "Late Edition."

Bartlett said the administration "will continue to work through the diplomatic initiatives" to convince Iran -- which Bush once called part of an "axis of evil" -- not to pursue nuclear weapons.

"No president, at any juncture in history, has ever taken military options off the table," Bartlett added.

Bush has warned Iran in recent weeks against meddling in Iraqi elections.

A former intelligence official says Hersh an American commando task force in South Asia is working closely with a group of Pakistani scientists who had dealt with their Iranian counterparts.

The task force, aided by information from Pakistan, has been penetrating into eastern Iran in a hunt for underground nuclear-weapons installations.

In exchange for this cooperation, Pakistani President Pervez Musharraf has received assurances that his government will not have to turn over Abdul Qadeer Khan, the father of Pakistan's atomic bomb, to face questioning about his role in selling nuclear secrets to Iran, Libya and North Korea.

Bush has already "signed a series of top-secret findings and executive orders authorizing secret commando groups and other Special Forces units to conduct covert operations against suspected terrorist targets in as many as 10 nations in the Middle East and South Asia," confirms a top White House source.

Defining these as military rather than intelligence operations will enable the Bush administration to evade legal restrictions imposed on the CIA's covert activities overseas.