A week into the war in Iraq, it's time to shelve the rosy scenarios and accept an unpleasant fact: The United States faces a long battle to defeat resistance fighters organized by the Baath Party and Saddam Hussein's secret police.

Even if U.S.-led forces achieve their goals on the main battlefields in coming days, as still seems likely, the guerrilla campaign will continue. That's because of the pervasive but largely clandestine system of political control that Iraqi dissident Kanan Makiya described in his book, "Republic of Fear."

It's also possible that U.S. and British intelligence were misled by the Iraqis into believing that many units wouldn't fight. A similar deception occurred at the end of the 1991 Gulf War. U.S. officials expected that a particular Iraqi general would lead a coup against Hussein, but it never happened.

The heart of the Iraqi political system is Hussein's Baath Party, which seized control in 1968. It's the only legal political organization in Iraq, and it maintains a network of cruelty and physical coercion throughout the country. Iraqis who challenge this system run the risk of arrest, torture and execution.

Saddam's Fedayeen, which has caused so much trouble in southern Iraq, is a Baath Party militia organized by the most ruthless of Hussein's sons, Uday. These warriors are said to be "stiffening" Iraqi military units and driving them into battles that, on their own, they might choose not to fight.

"With our party methods, there is no chance for anyone who disagrees with us to jump on a couple of tanks and overthrow the government," Saddam Hussein explained in 1971, according to Makiya.

The Iraqi system is reminiscent of the political commissars Joseph Stalin used to intimidate and galvanize the Soviet army during World War II, with political troops often taking positions behind the regular army in battle and shooting any laggards. Hitler used a similar system, with SS and other Nazi Party units stiffening the will of a professional military that had increasing doubts about the war.

The pervasiveness of the Baath organization, which has operatives and informers on nearly every street and in most villages, helps explain why the Iraqi population has not greeted the U.S.-led coalition as liberators. Patriotic Iraqis may resent the U.S.-led invasion, to be sure, but they also live in a permanent climate of fear and suspicion.

Four Iraqi farmers I interviewed in the southern part of the country last weekend each said they had relatives who had been executed by Hussein's secret police. The four, all Shiite Muslims, said they would be happy to see Hussein toppled. But they also said they were mistrustful of the United States because of their experience in 1991, when America encouraged a Shiite uprising only to leave it to a bloody fate, in which some 50,000 people were slaughtered.

Even in the town of Safwan, just across the border from Kuwait, the local Baath Party headquarters was said to be active this week plotting attacks against U.S. and British troops. The Baath Party and fedayeen have also been leading resistance in Basra. To break the party's control in that city, British commandos seized the top Baath official there and American planes destroyed the party's Basra headquarters. These moves may have encouraged the "limited revolt" reported in Basra; they also illustrated the tough fight that lies ahead.

The Baath operatives fight so hard because they have nothing to lose. They believe they will be slaughtered by revenge-minded Iraqis after the war.

Much like the Leninist revolutionaries who seized control of Russia in 1917, the Syrian intellectuals who founded the Baath Party in 1947 believed that their goal of Arab unity justified any means, no matter how vicious. "When we are cruel to others, we know that our cruelty is in order to bring them back to their true selves, of which they are ignorant," argued Michel Aflaq, the party's co-founder.

When the Baath Party seized power in Iraq in 1968, Hussein was one of its toughest clandestine operatives. In 1969, according to Makiya, Hussein handpicked the head of internal security, a man named Nadhim Kzar, who made a hideous practice of extinguishing his cigarettes on the eyeballs of those who refused to talk. The regime conducted its interrogations in a prison that Iraqis called "The Palace of the End."

As with Stalin and Hitler, the very brutality of the Iraqi leader has helped create a bizarre mystique -- a culture that mixes fear and adulation. To Iraqis, Hussein has become a kind of human god -- vengeful, unpredictable, implacable. This is the adversary the U.S.-led coalition has taken on. No wonder it won't be a short or easy fight.