F-16 pilot Maj. Kevin Jens of the 419th Fighter  Wing from Hill Air Force Base greets his  18-month-old son Eric, right, wearing his hat, as daughter Lexi, 4, waves upon his arrival at Salt Lake International Airport on Thursday, April 17,  2003, in Salt Lake City. Jens was one of more  than a hundred reservists who returned home from deployment in the war on Iraq. (AP Photo/Kent C. Horner)

WASHINGTON - Americans used to worry about the "domino theory" - one country going communist and others tumbling the same way. Now some wonder whether the United States, toppling two governments in two years, is playing dominoes, too.  In the first flush of victory in Iraq, U.S. officials began talking tough about Syria, across the border from a massive American invasion force. Worldwide, the threats of terrorism and weapons of mass destruction remain - when it comes to "axis of evil" countries, after all, it's one down and Iran and North Korea to go.  America's armed forces, by any measure, are on a roll.  So is it on to Damascus? Tehran? Or Pyongyang?  Few think so.

For the first time since Sept. 11, 2001, the United States seems ready to give peace a chance, if terrorists will let it. 

Its guard is up. But President Bush's appetite for another pre-emptive war is evidently down, at least in the short run. 

"He will want to take a time out, develop strategy, do a diplomatic 'shock and awe,'" said Simon Serfaty of the Center for Strategic and International Studies. "This overwhelming display of forces awed the states that wish evil on the United States." 

And with U.S. forces still tied down in Afghanistan and just beginning the struggle for order in Iraq, "there are only so many wars you can wage at the same time." 

The prospect of an America aroused to right every wrong worries plenty of people overseas. Russia's defense minister did not wait for the Iraq war to end to voice his concern. 

"Today the United States doesn't like Iraq," Sergei Ivanov said. "Tomorrow Syria, then Iran, North Korea and then what - everyone else?" 

Even some hawks worry about conflagration spreading across the Middle East if the United States should pursue another target in the region. Analysts say world reaction would be incomparably worse than in the heated leadup to the Iraq war. 

And they say invasions are simply too costly in lives and treasure to continue carrying out, again and again, absent direct provocation. They disagree, however, how tough some of these countries would be to beat. 

Afghanistan and Iraq will go down as among the least costly U.S. conflicts in modern history but sometimes vastly overmatched nations can exact a heavy price, even win. Vietnam, in a region once at the core of domino-theory fears, showed that. 

So far the Bush administration is sticking to its position that North Korea and Iran can be made less threatening through negotiation. Both countries have made positive gestures since U.S. and British forces routed their Iraqi opposition - most notably North Korea, which is renewing talks over its nuclear program. 

With Secretary of State Colin Powell planning to visit Syria, diplomacy has become the leading course to discourage that country from becoming a haven for terrorists or fleeing Iraqi America-haters. Washington also accuses Syria of having a chemical weapons program, which Damascus denies. 

"I think we have diplomatic opportunities in each one of these countries, and we're not on the brink of war with any," said national security analyst Peter Brookes of the Heritage Foundation, a conservative policy group often close to the Bush administration's thinking. 

A Washington Post-ABC News poll out Friday indicated a majority of Americans think North Korea is a serious threat. But sentiment was strongest for a peaceful solution. 

Both Iran and Syria have international standing that eluded Saddam Hussein's Iraq or Afghanistan of the Taliban era, analysts said - as well as terrorist ties that go at least as deep as Iraq's did. 

"Going to war with Syria would be tantamount to going to war with all the countries of the Middle East," Serfaty said. 

North Korea is largely isolated but highly militarized and capable of causing massive destruction in South Korea's capital, Seoul, in short order. 

A closer look: 

SYRIA: 

Syria's military resembles Iraq's prewar force but is smaller, with about 250,000 in uniform, said a U.S. defense official, discussing intelligence information on the condition of anonymity. It has Scud missiles, about 450 fighter aircraft and old tanks. 

Syria could undermine the U.S. position inside Iraq by serving as a staging ground for Arab attacks or by exporting jihad to its neighbor, said James Phillips, a Middle East analyst at Heritage. "That's why the administration wants to warn Syria now, while it has maximum military leverage." 

IRAN:

"Those guys can fight," Serfaty said. "It would be unthinkable we would start a war against Iran in the near future" - at least not until Iran verifiably develops a nuclear weapons capability. 

Phillips put less stock in Iran's military, saying it has been sapped by revolution and the 1980s war with Iraq. "The problem with Iran is that it has a web of terrorist groups it could use to indirectly target the United States," he said. 

But he said the administration has concluded "Iran could evolve according to its own methods into a state that does not support terrorism." 

NORTH KOREA:

A huge army and artillery inventory, an ambitious missile program and the possibility it already has a few nuclear weapons make North Korea an unlikely military target unless it does something first. 

"They may not be eating much," Serfaty said, "but they are well armed and willing to fight."