Americans were understandably shaken by the two suicide car bombings last week that killed seven U.S. soldiers. Both attacks relied on what appeared to unlawful deceptions: Friday's bombing, at a checkpoint 130 miles northwest of Baghdad, reportedly involved a woman crying in distress to lure soldiers; the earlier attack near Najaf was apparently carried out by a noncommissioned Iraqi army officer posing as a taxi driver. These attacks should not surprise us: The annals of modern warfare are filled with examples of regular and irregular forces who rely on stealth and civilian disguise to counter the superior force of an invading or occupying power.

But if guerrilla tactics are commonplace in contemporary interstate wars, the use of suicide bombers dressed as civilians is not (although they are a familiar feature of the Palestinian-Israeli conflict). To be sure, Japanese kamikaze pilots undertook suicide missions during World War II, targeting American ships. But the pilots' planes were clearly identifiable as enemy aircraft -- and so their suicidal missions breached no rule of international law.

As if raising the stakes, Iraq's information minister vowed on Friday that there would be an "untraditional" attack on allied forces who had just secured Baghdad's airport. The minister, Mohammed Saeed Sahhaf, said the attackers would mount "martyrdom operations in a very new, creative way."

Many of those who are commanding the U.S. forces would be familiar with guerrilla tactics, having confronted them when they were young soldiers in Vietnam. Concealing weapons and feigning civilian status, Viet Cong guerrillas were able to launch surprise attacks -- and then vanish instantly.

The Viet Cong could trace their military lineage to the Spanish Maquis, who waged clandestine warfare against Napoleon's armies during the Peninsular War between 1808 and 1814. Refusing to fight in orderly formation or uniform, the Maquis -- the prototype guerrilla force -- harassed and sniped at their enemy, rarely took prisoners and depended on Spanish civilians for supplies and other logistical support.

Since 1945, British forces have battled irregulars in Palestine, Borneo, Aden, Northern Ireland and elsewhere. These guerrillas, like today's Iraqi irregulars, carried out ambushes and then melted into local communities, imperiling civilians in the vicinity.

Specialized units of regular U.S. and British armed forces have also relied on guerrilla-style tactics. During World War II, British Commandos and American Rangers assisted indigenous resistance movements behind enemy lines in German-occupied Europe and elsewhere. Today, U.S. Special Forces are undertaking guerrilla-style missions in Iraq.

Some guerrilla attacks, whether considered lawful or not at the time, have become the stuff of heroic lore. Military historians credit resistance movements in occupied France, Yugoslavia and the Philippines with hastening the defeat of Germany and Japan in World War II. In Yugoslavia, Tito's Partisans pinned down thousands of German troops who could otherwise have been deployed against allied forces.

It is not hard to see why Iraqi forces, like other irregulars before them, have resorted to guerrilla tactics. Stealth, subterfuge, hit-and-vanish tactics and other standard guerrilla stratagems might offset the advantages of outsized, high-tech enemy forces. They may even be perfectly lawful. For example, an ambush by itself does not breach the laws of war. But an ambush by combatants dressed like civilians is clearly illegal. International law makes distinctions between lawful ruses -- such as the use of camouflage, decoys and misinformation -- and unlawful deceit. The law prohibits the killing or injuring of the enemy by treacherous or perfidious means: by feigning surrender or incapacitating wounds and then opening fire, for example.

Some of the tactics reportedly employed by Iraqi forces, like deploying bombs on combatants while posing as civilians, clearly violate the laws of war. What's more, they are war crimes, prohibited by The Hague regulations of 1907 and customary law -- the body of international law that binds all countries. Iraq's vice president, Taha Yassin Ramadan, proclaimed what amounts to a criminal policy when he warned that attacks like the first suicide bombing -- involving a combatant feigning civilian status -- would be "routine military policy" until the United States ends hostilities in Iraq.

By erasing visible differences between civilians and warriors, these tactics threaten one of the most basic rules governing the conduct of hostilities: Civilians must be spared the ravages of war. For centuries, customary international law has required military forces to direct their fire at combatants and not civilians. In the jargon of the law, which binds every country -- including Iraq -- combatants must scrupulously respect the "principle of distinction." Combatants who disguise themselves as civilians -- like the Iraqi officer who pretended to be a taxi driver -- undermine this principle, making all civilians potential combatants in the eyes of enemy soldiers.

And of course that's the point. By blurring the line between civilians and combatants, Iraq taunts coalition forces with a devil's dare. Every Iraqi suicide bomber clad in civilian dress tempts American forces to respond to the next suspicious-looking Iraqi with deadly fire. Jittery U.S. forces did just that when they opened fire on a civilian van that ignored warning shots. "You just [expletive] killed a family!" the anguished captain in charge was quoted as saying. As many as 10 civilians were killed, five of them children; two others were wounded. The dilemma for coalition forces is obvious and excruciating: Under marching orders to spare civilians from hostile fire, British and American forces find themselves under attack by fighters masquerading as civilians.

In these circumstances, some now wonder whether codes designed to spare civilians from the ravages of war are dangerously outmoded, forcing coalition forces to fight with one hand tied behind their backs, while Iraqi forces flout the rules of warfare. (Indeed, the very project of seeking to constrain the conduct of war through humanitarian law strikes some as hopelessly quixotic.) But the rules of modern warfare are anything but a suicide pact. Military forces must take care to distinguish civilians from combatants, but of course they may defend themselves from attack by persons posing as civilians.

The danger for U.S. forces will lie in the temptation to overreact to potential threats, firing on civilians because they might be combatants, when sound precautions could have mitigated the risk. Such responses may protect Americans in the immediate term but imperil them in the longer term and prolong the conflict in Iraq. Images of Iraqi civilians killed by American soldiers will further alienate Iraqis who remain unpersuaded that Americans are their liberators, and win new recruits to Saddam's side.

The United States will soon confront another set of challenges, relating to thousands of Iraqis captured by coalition forces. Since the 19th century, one of the most controversial issues at conferences convened to draft and revise the laws of war has been whether to grant irregular forces a status comparable to that enjoyed by regular armies. As "lawful combatants," the latter enjoy the so-called combatant's privilege -- essentially a license to kill enemy combatants without risking prosecution for lawful acts of war -- and are entitled to prisoner-of-war status if captured by enemy forces. The vexing question has been when to extend these privileges to irregular forces.

Despite the contributions of irregular forces to the Allied war effort during World War II and their ruthless treatment by Axis captors, diplomats continued, even after the war, to set a high bar for irregular forces to qualify for POW status in any future conflict. Under the 1949 Geneva Convention dealing with prisoners of war, irregular forces qualify for POW status only if they belong to a party to an interstate armed conflict; operate under responsible command; wear a distinctive emblem recognizable from a distance; carry their arms openly; and conduct their operations in accordance with the laws of war. (A newer convention adopted in 1977 lowers the bar somewhat, allowing irregulars to claim POW status even if they blend into civilian communities while off duty, as long as they distinguish themselves during actual combat. But neither the United States nor Iraq is a party to this protocol.)

In this way, international law offers an inducement for irregulars to follow the basic ground rules of humanitarian law. Being a guerrilla isn't a war crime. Using civilians as human shields is -- and disqualifies irregular forces from enjoying the privileges accorded lawful combatants.

So far, it appears to be Pentagon policy to treat Iraqi prisoners as POWs unless it is determined (in accordance with Article 5 of the Third Geneva Convention) that they are not lawful combatants. This approach is a welcome departure from the administration's policy toward detainees in Guantanamo, who were denied POW status without recourse to a competent tribunal.

Like members of al Qaeda, Saddam Hussein's Fedayeen fighters would surely flunk the stringent tests irregular forces must pass to qualify as lawful combatants. But the Third Geneva Convention would accord POW status to other categories of Iraqi fighters, such as civilians who spontaneously take up arms in self-defense, so long as they carry their arms openly and respect the basic rules of humanitarian law.

The same convention accords POW status to captured members of Iraqi regular armed forces, including Republican Guard units, even if they violate the laws of war. The U.S. government undermined this rule when it refused to recognize members of Taliban armed forces as POWs. Its position was controversial and rightly so: The Geneva Convention plainly states that members of the armed forces of a party to an interstate conflict are entitled to POW status. Instead, Washington applied a more stringent standard that the convention makes applicable only to irregular forces.

That approach troubled the International Committee of the Red Cross and various U.S. allies -- and it was not in America's best interest. Rewriting the rules of war when compliance seems inconvenient invites other countries to do the same. Wrenching images of American prisoners now in Iraqi hands provide painful reminders that it serves our interests as much as our values to nourish a scrupulous regard for the letter of the law. Diane Orentlicher is a professor of international law and director of the War Crimes Research Office at American University. Robert Goldman is a professor of law and Louis C. James Scholar at American University.

Iraqi prisoners are escorted out of Basra by U.S.-led forces.