At a time when the war in Iraq is as unpopular as ever and Congress is searching for ways to turn back President Bush's 21,500-troop surge, tensions with neighboring Iran have escalated.

Bush recently told NPR that "if Iran escalates its military action in Iraq to the detriment of our troops and/or innocent Iraqi people, we will respond firmly." Though the president has made pains to say that the heated rhetoric is not a means of laying the groundwork for another battlefront, on Monday, The New York Times reported on a long-gestating report that the administration said proves that Iran is supplying some of the deadliest munitions being used against U.S. forces in Iraq. The report has been likened in some reports to the one about alleged weapons of mass destruction that the White House used more than four years ago as a precursor to war with Iraq.

Is it possible that the U.S. is about to open a third front in the war on terror at a time when, by all accounts, the military is already stretched to breaking point?

The evidence has been growing daily:

» The U.S. has begun beefing up its presence in the Persian Gulf citing Iran's involvement with Iraq's Shiite militias and the country's ongoing nuclear ambitions, sending a second aircraft carrier to the region and deploying Patriot anti-missile batteries. In seeming retaliation, during war games last week, Iran successfully tested land-to-sea cruise missiles intended to show that it had the capability of hitting "big warships in all of the Persian Gulf."

» The #2 U.S. general in Iraq, Lieutenant General Raymond Odierno, told USA Today that Iran was supplying Iraqi Shiite militias with powerful weapons, including Soviet Katyusha rockets and armor-piercing, rocket-propelled grenades.

» On January 20, militants captured and killed four American soldiers in a raid in Karbala, killing a fifth in a firefight. A U.S. defense official told The Associated Press that it's possible "Iranian agents either executed or masterminded the attack," based on the evidence of the "sophisticated and unusual" weapons that were used, which included uniforms that may have been American.

» Senior Pentagon officials told the Los Angeles Times that the Air Force is considering more forceful patrols on the Iraqi side of the border with Iran to cut off weapon-smuggling.

» The Associated Press recently reported that Iran is feverishly laying down piping and electric cables for its underground uranium enrichment plant, with hundreds of workers being employed to move ahead quickly with a program that could be misused to make nuclear arms. The move further escalates the tensions between Iran and the international community over its alleged drive to build nuclear weapons.

» Iran's Supreme Leader, Ayatollah Ali Khamenei, said last week that if the United States attacked, Iran would strike American interests worldwide. Iran also accused the U.S. of abducting an Iranian diplomat in Baghdad last week; U.S. officials would not even confirm a kidnapping had taken place.

» Perhaps most damningly, a recent National Intelligence Estimate report claims that the most lethal weapons used against American troops in Iraq, an armor-piercing "explosively formed penetrator" used as a roadside bomb, is being supplied by Iran to Shiite militias. According to a New York Times review of the report, attacks using this kind of bomb — which fires molten chunks of metal that cut through armor when exploded — have doubled in the past year. "In the last three months of 2006, attacks using the weapons accounted for a significant portion of Americans killed and wounded in Iraq" and contributed to 170 American deaths over the past three years.

The link to Iran is reportedly based on analysis of captured devices, serial numbers, examination of explosion debris and intelligence about the training of Shiite militias and other militants who are believed to be working at Iran's behest. Experts also point to the sophistication of the bombs, the raw materials and expertise needed to build them as proof that Iran is behind the devices, as Iraq doesn't have the capabilities or raw materials to build them.

In what some say is a troubling similarity to the shaky WMD "proof" the Bush administration used to launch the war in Iraq, the report's assertion that Iranian leaders authorized the smuggling of the weapons into Iraq for use against Americans comes from an extremely vague source: an anonymous "inference based on general intelligence assessments." Iran has denied the report's findings.

So, does all of this mean we are headed toward an inevitable military showdown with Iran? Possibly, said Newsweek senior editor Michael Hirsh.

"The main reason we're hearing so much about Iran is that it became apparent last fall that the diplomatic strategy on the nuclear issue was not getting anywhere," said Hirsh, one of the magazine's experts on international affairs (see "Iran Doesn't 'Give A Damn' About U.N. Pressure On Nuclear Program"). "We had gotten a United Nations Security Council Resolution [on the nuclear issue], but it was very weak. And at the same time the Bush administration became concerned about out-of-control violence in Iraq and Iranian encouragement to increasingly significant and powerful Shiite militias in Iraq."

Hirsh said the White House began to sense that Iran was not paying any price for its involvement in Iraq, and thus has decided to "get tough" with Iran. But is this policy intended to lead to negotiations, war, or both? Based on his reporting, Hirsh said the saber-rattling by the U.S. — including the new carrier group in the Gulf and the possible airstrikes on the border — is not necessarily an inevitable run-up to a war with Iran, but a tactic designed to make Iran think twice about how far it is willing to test U.S. patience.

"I don't think Bush has decided on a war [with Iran]," Hirsh said. "I think a contingency plan is under way for dealing with Iran through military strikes, but this would be an air campaign with special forces. It would be nothing like the invasion of Iraq because of the fear that it could cause a more regional war. Wars start accidentally and the fear is, maybe we kill some operatives we claim are from Iran that are helping the Shiites and they turn out to be diplomats or have a legitimate purpose — and [then] Iran retaliates. There is no question that an action like that could lead to a larger-scale attack that could kill a lot of Americans."