BEIRUT, 6 August 2005 — As Iraq’s insurgents score one success after another, they are rewriting the rules of modern guerrilla warfare.

They have ignored the lessons that guided most rebellions of the 20th century: Try to win broad public support; create a political wing; present an alternative system of governing; and build international legitimacy. The Iraqi insurgency also has no charismatic leader, no clear chain of command, and not even a cohesive ideology.

Still, the guerrillas have managed to spread chaos across Iraq. They have nearly halted reconstruction, hamstrung the country’s fledgling security forces and pinned down the most powerful military in the world. The insurgents have shown a remarkable ability to adapt their tactics to inflict maximum damage against both civilian and military targets.

US officials say guerrillas are using a variety of mechanisms to trigger bombs, applying large amounts of explosives and experimenting with new techniques to penetrate US armor. In the latest example, 14 Marines were killed Wednesday when their patrol vehicle struck a powerful roadside bomb in western Iraq.

“This is a very lethal, and unfortunately, adaptive enemy that we are faced with inside Iraq,’’ Brig. Gen. Carter Ham said in Washington after Wednesday’s attack.

But while the guerrillas are skilled at modifying their military tactics, they seem indifferent to the political models of past insurgencies. Most successful rebellions in the past century shared two traits: They had widespread public support and a well-articulated political agenda, which usually appealed to nationalist sentiment. In Iraq, the insurgents have neither.

It could be a new kind of insurgency, one which does not have enough support or a clear political program to rule Iraq but is also difficult to defeat because it does not care about civilian casualties and destroying the country’s infrastructure. In this context, past experience in Vietnam and elsewhere would offer the United States few lessons about how to fight back.

Since a wave of car bombings began in August 2003, the insurgents have shown a willingness to kill civilians indiscriminately. With each new bombing that targeted a market, a mosque, or a wedding party, the guerrillas lost another chance to win Iraqi hearts and minds.

“These so-called freedom fighters are terrorizing the Iraqi people. They are killing many more civilians than American soldiers,’’ said Ali Abdel Ameer, an Iraqi writer and political activist. “They will never have a large following because most Iraqis find their actions abhorrent.’’

Since a renewed wave of violence in early April, insurgents have killed more than 2,700 Iraqis, according to the Iraqi Defense Ministry. Half of those killed were civilians, and the rest were members or recruits of the country’s security forces.

Even the bloodiest rebellions of modern times did not target civilians the way the insurgents have in Iraq. In Algeria, for example, rebels fighting against French colonial rule in the 1950s and 1960s adopted a classic guerrilla tactic:

They provoked the occupying troops to use excessive force and kill thousands of civilians. That prompted a public backlash and international condemnation of French actions. The French eventually withdrew from Algeria, after as many as one million people had been killed.

The Algerian guerrillas did kill fellow countrymen, but they were usually people suspected of collaborating with the French or civilians caught in the crossfire. The rebels also bombed cafes and markets, but they chose targets frequented by French soldiers and colonials.

“Traditionally, insurgents need at least passive support from the local population,’’ said Kamil Tawil, a Lebanese historian and expert on militant movements.

The guerrillas now fighting in Iraq appear to have ignored even the lessons of Iraq’s past rebellions. During the revolt of 1920, both Sunni and Shiite Muslims rose up against the British occupation of what was then Mesopotamia. The uprising, in which 6,000 Iraqis and 500 British soldiers were killed, failed to dislodge British rule. But it demonstrated the potential of Sunni— Shiite cooperation, and it has grown in political mythology to become the foundation of Iraqi nationalism.

Today, the insurgency is being driven by Iraq’s Sunni minority. Most of those killed by insurgent attacks have been Shiites and Kurds, and that has turned those communities against the rebellion.

Even if they are able to drive out US troops, the guerrillas are unlikely to gain control over all of Iraq without support from the Shiite majority.

Some segments of the insurgency could be hoping to foment a sectarian war that would lead to the partitioning of Iraq into Sunni, Shiite and Kurdish regions.