The warnings were there that far-right fury would explode. Now a local sideshow has become a national emergency, says Phil Reeves
He was as tough a federal agent as you are ever likely to meet, a wiry man who had seen action in Northern Ireland and had been in the front line of America's war on the narcotics trade. But after four days of digging for his dead partner in the rubble of the Oklahoma City bombing, he finally broke down and cried uncontrollably.

"If I get a chance to kill Timothy McVeigh, I will do it," he said, his eyes puffy with weeping. He is not the only Oklahoman who has openly threatened to kill the 27-year-old whom the US authorities believe carried out the bombing. But his threat was more serious than most. He opened his tartan shirt, to reveal a pistol. "I would use this if I had a chance, believe me."

Six days after the disaster, Americans do not bother to wonder if Timothy McVeigh, the former US soldier arrested on the day of the bombing, is innocent. But they have been asking questions. How were his extremist political views nurtured? How, for that matter, did America spawn such a cluster of fanatical paramilitary groups, who may -or may not - have played a role, but whose members share the same crazed philosophy?

In rural America, Timothy McVeigh would not have been considered particularly odd. Every weekend the desert canyons and mesas outside Kingman in northern Arizona - his last official address - echo with the sound of gunfire as rural white males test their latest high-powered weaponry. Few locals would have been surprised by the sight of him striding around his trailer park, en route to a tree-shooting spree in the wilderness, wearing camouflaged army fatigues tucked into his black combat boots.

When McVeigh and his friends in Michigan - Terry and James Nichols, now held as probable material witnesses to the Oklahoma bombing - started mixing household chemicals in plastic milk bottles and detonating small explosions with great glee, the neighbours barely raised an eyebrow. They were simply good 'ole country rednecks, local crazies having some fun on their farm.

Nor is there anything unusual about his political views - which are said by the FBI to be extremely right wing. Visit almost any small town bar, especially in the western US, and you can easily find an angry American male spouting forth about a federal conspiracy on a variety of fronts - from excessive taxation to Congress's ban on certain assault weapons, or restrictions on the right of hunters to shoot mountain lions. In the last few years, such views have been percolating into mainstream politics, not least because of the Republican Party's (and, in particular, Newt Gingrich's) love affair with the nation's army of right-wing radio hosts, many of whom go perilously close to advocating the use of violence to solve political problems.

It has, for example, infiltrated into the anti-immigration debate which spawned California's Proposition 187, a law passed by public ballot which bans illegal immigrants from receiving health care and education. The legislation is still tied up in the courts, but a nationwide drive has begun to introduce similar measures in other states. While its supporters include many ordinary Americans, it is far from uncommon to hear its advocates outlining the same anti-government views as the diverse mix of militant groups - from the Patriots to the Michigan Militia - who now find themselves at the centre of international attention as a result of the bombing.

Despite this, America's media - and, it seems, its law enforcement agencies - have taken a highly complacent attitude to the rise of the far-right paramilitaries, often writing them off as paranoid weapons-obsessed nutcases, who are no more deserving of column inches than those who believe the US government has captured aliens (a not uncommon article of conviction among the movement's devotees).

Several less radical militiamen say they called the FBI in recent months and warned that there would be some kind of attack, only to be given the brush off. In Nevada's Nye County a series of small bombs exploded last month at US Forest Service installations in the Toiyabe National Forest: little national attention was paid to them, or to the news that the children of federal employees were being harassed at school - violence which was attributed to a so-called Sagebrush Rebellion mounted by loggers, miners and farmers frustrated by the federal government's huge landholdings, and its plethora of environmental laws. Though the incidents were small, they were indicative of an alarming trend that was being widely ignored.

This dismissive view is scarcely surprising, given the ludicrous views of many elements involved. At a "Soldier of Fortune" convention in Las Vegas several years ago, the dozens of men clumping around casino foyers and palm-lined gardens in boots and khaki clothing included plenty of "New World Order" fantasists, raving about a Zionist conspiracy to establish a global government. At best their members seemed highly eccentric - for instance, Paul Bible, an Arizonan who kept a camouflaged truck loaded with food, ammunition and supplies in his backyard against the day when the federal government might invade. At least two of those attending were working police officers from Los Angeles.

As the Oklahoman bombing has made clear, the paramilitary right has been on the rise in the past few years, becoming part of a larger political movement that is rapidly getting organised. It has many shades - from outright racism to anti-tax movements, but it centres on a loathing of the federal government in general, which some elements aspire to overthrow, and a particular hatred of Bill Clinton. (The President is so vilified among some of the militiamen, who include ex-servicemen infuriated by his support for gays in the ranks, that they use images of him and his wife, Hillary, as targets on shootings ranges.)

As their numbers have grown - estimates vary from 10,000 to 100,000 - so have their organisational skills, aided by new technology. The Internet has an electronic bulletin called "alt.activism.militia" which has been seething with cyber-babble about the wicked ways of the US government, and the type of weapons that should be deployed against it. The advent of the computer data networks, which appeal to the average militiaman's love of the covert and conspiratorial, have linked groups together, providing them with an ideal forum in which to indulge their paramilitary fantasies.

According to the Wall Street Journal, it is even possible for the computer literate to access a document called the "Terrorist's Handbook", which describes how to go about making bombs, and offers advice about the best way to filch the materials from university laboratories. The Patriot Archives included a "Proclamation", with a 1994 copyright, announcing that 19 April was to be called Militia Day, and would be devoted to paramilitary training and parades: "All able-bodied citizens are to assemble with their arms to celebrate their right to keep and bear arms and to assemble as militias in defence of the Republic."

19 April - the day of the Oklahoma City bombing - has become a red-letter day for the more radical elements of the militant counter-culture. Its significance was explained by a newsletter, published last month, by the Militia of Montana: 19 April 1775 was the date of the battle of Lexington, a clash between colonialist Minutemen and the British which helped spark the American revolution; on 19 April 1943 "Warsaw burned"; 19 April 1992 was the date of an aborted raid by agents from the Bureau of Alcohol, Tobacco and Firearms on Randy Weaver, a white supremacist whose wife was shot by an FBI sniper during a siege in the mountains of Idaho. And on 19 April this year - only 12 hours after the bombing - Richard Wayne Snell, another white supremacist, was executed in Arkansas for murdering a Jewish businessman and a black police officer.

But most of its symbolism resides in the fact that it is the second anniversary of the dbcle at Waco, Texas, in which 86 people died when the FBI stormed into the Branch Davidians' fortified compound, using tanks and tear gas. For the more extreme militiamen, it was tantamount to a declaration of war - final evidence of the federal government's determination to seize the public's guns. David Koresh, the Davidian's self-styled messiah, had a vast arsenal of weapons. When Timothy McVeigh was arrested on the day of the blast, documents were reportedly found in his car vowing revenge for the Waco incident.

It will be many months before America discovers whether it was he who committed the worst act of domestic terrorism in its history, if he survives at all - he is in real danger of being shot, such is the fury over the bombing. It is not even clear exactly what relation he and his associates had, if any, with the paramilitary far right. But if any benefit can be drawn from the ghastly cocktail of fertiliser and hatred that blew up in Oklahoma last week, it is that the nation has finally woken up to a deeply paranoid and dangerous mentality at its very core.