June 19 (Bloomberg) -- Fred Thompson, who may join the Republican presidential race, said today that the U.S. and its allies should consider a blockade against Iran before military action to curb the nation's nuclear ambitions.

``A blockade would be a possibility if we get the international cooperation,'' the former Tennessee senator said in a speech at the Policy Exchange, a political research foundation, in London. ``If we were all reading off the same page and saw the nature of the threat, that would be one way to make sure that we didn't have to go to the military option.''

Thompson didn't give details about his view for a possible blockade or discuss whether it should be limited to naval power or extended to cover Iran's land borders with Afghanistan, Pakistan, Turkey or Azerbaijan.

The remarks are among his first on foreign policy since he quit as an actor on the ``Law & Order'' television drama and formed a committee to raise money for a possible presidential campaign. President George W. Bush has expressed concerns that Iran's nuclear program may be aimed at building a bomb.

Thompson, 64, served as a Republican senator for Tennessee from 1995 to 2003 then played a New York City district attorney on ``Law & Order.'' Thompson's unapologetic support for American military power helped boost his popularity in the field of Republican presidential contenders to No. 2 behind New York Mayor Rudolph Giuliani, according to a USA Today/Gallup poll.

Iran's `Pirate'

Thompson in recent weeks has said he supported the increase in American forces deployed in Iraq and described Iranian President Mahmoud Ahmadinejad as a ``pirate.'' Today, he expanded on his views about Iran in particular.

``When the president of Iran shares his nightmare visions before cheering crowds, those are not just a fanatic's version of an empty applause line,'' Thompson said. ``The only safe assumption is that he means it.

``If we know anything from modern history it is that when fanatical tyrants pledge to wipe out an entire nation, we should listen. We must gather our alliance and do all in our power to make sure that such men do not gain the capability to carry out their evil ambitions.''

Thompson's appearance in London, largely covering trans- Atlantic issues, was his first speech abroad since he formed his presidential committee on June 1.

He said he would meet former U.K. Prime Minister Margaret Thatcher tomorrow and expressed great admiration for her.

``We count ourselves lucky to call the United Kingdom our closest ally and we are proud to call you our finest friend,'' Thompson said.

A USA Today/Gallup survey last week of 393 Republican or likely Republican voters showed Giuliani leading the field with 28 percent, followed by Thompson with 19 percent and Senator John McCain with 18 percent.

To contact the reporter on this story: Francis Harris in London at fharris4@bloomberg.net.

Last Updated: June 19, 2007 12:24 EDT