By JIM KUHNHENN
The Associated Press
Friday, October 12, 2007; 10:27 PM

WASHINGTON -- Republican presidential candidate Mitt Romney is airing a new television ad in Iowa casting himself as tough on terrorism, confronting one of the central themes of rival Rudy Giuliani's campaign.

In the 30-second ad, the former Massachusetts governor promises to strengthen U.S. intelligence agencies, increase the size of the military by at least 100,000 troops and monitor calls made to the United States by suspected al-Qaida associates.

"And we can and will stop Iran from acquiring nuclear weapons," Romney says.

The ad, which aides said had been prepared some time ago and will run statewide, is airing after Giuliani pounced on Romney's debate answer this week on whether to seek congressional authority before initiating military action against Iran.

The ad also comes as Democratic lawmakers are moving a government eavesdropping bill through the House of Representatives. The Bush administration objects to the legislation because it does not give retroactive immunity to U.S. telecommunications companies that assisted the government conduct surveillance without court orders.

"It's this century's nightmare, jihadism _ violent, radical Islamic fundamentalism," Romney says to the camera from the yard outside his Belmont, Mass., home.

"Their goal is to unite the world under a single jihadist caliphate. To do that, they must collapse freedom-loving nations like us."

Romney is expected to discuss similar themes of national security and terrorism when he speaks before the Republican Jewish Coalition on Tuesday in Washington.

Giuliani, who has capitalized on his role as New York mayor during the 2001 terrorist attacks, and presidential candidate John McCain have both criticized Romney for suggesting that lawyers would have a role in determining whether Congress needed to approve a military strike against Iran's nuclear sites.

During a debate this week, Romney said he would talk to attorneys about Congress' role, but added: "Obviously the president of the United States has to do what's in the best interest of the United States to protect us against a potential threat."

In a letter to the editor of the Wall Street Journal on Friday, Romney defended his position, saying a president must act to protect Americans. "As to what involvement Congress may have, that's a matter for legal consideration," he wrote.

"When time and circumstances permit," he added, "I would indeed seek the involvement of Congress as required by law and the Constitution."

The Democratic National Committee said Romney's ad presents an oversimplified view of conflict in the Muslim world.

"Mitt Romney's new ad shows that he still has no plan for Iraq, no plan for capturing Osama bin Laden and no understanding of the threat facing our country," said Democratic National Committee spokesman Damien LaVera.