EVERY so often Americans work themselves up into a collective lather about crime. This holiday season they are positively in a frenzy. At first glance, the reasons are not obvious. True, levels of violent crime are disturbingly high. But they have been that way for years, so why has outrage erupted now? The statistics suggest, if anything, cause for optimism: every major category - murder, robbery, rape, car-jacking, kidnapping - has declined, albeit slightly, since the beginning of the decade. What makes the timing of the current anti-crime fever even stranger is the absence of campaign rhetoric. Law-and-order, to be sure, was a major issue in mayoral and gubernatorial races last month. (In New York City, which put an ex-prosecutor into office, it was the issue). But there were only a few such races around the country and they are already long forgotten. No, we can't blame it on fear-mongering politicians. If congressmen are falling all over themselves to look tough on crime it is because they are following, not leading, public opinion. Nor can we easily blame the media for whipping up hysteria. Yes, tabloids and so-called ''reality-based'' television are still soaking up blood like a police blotter, but that's just entertainment, right? After all, someone must be jacking up the Nielsonratings. If not, then, a soaring crime rate or manipulation by vote-hungry politicians and profit-hungry media moguls, how do we account for the new public hue and cry against violent lawlessness? There are answers. Here are three. The first is accumulative: the crime rate may be consistent, but consistent mayhem is still mayhem. Significant portions of urban America are genuinely out of control, and have been for at least a decade. Congress can mandate stiffer penalties and more money for prisons, but the astounding fact remains that the US already has incarcerated a larger percentage of its population than any country in the world. Reason number two: the crime is getting younger. Both as victim and perpetrator, youth is claiming a larger share of the criminal pie. It is hard to say which is more horrifying, a couple of 13-year-olds who commit armed robbery and murder all in a day's work, or a 12-year-old girl who is abducted from her home, raped and murdered while her parents sleep. The homicide rate has doubled among 10 to 14-year-olds in the last 20 years and is the leading cause of death among 15 to 19-year-old blacks. And surely it is no less unsettling that the suicide rates for these age groups have tripled and doubled, respectively, over the same period. A third reason for growing alarm must be the changing quality of crime, which I would summarise with three ''R's'': randomness, remorseless and rage. Though Colin Ferguson made a list of the people, and kinds of people, he hated, in the end he just walked along the corridor of a New York commuter train last week and methodically fired - left, right, left, right - at whoever happened to be sitting in front of him. The final tally: six dead, more than a dozen wounded. Similar random rampages, some of them ending in suicide, have multiplied in the last few years. Here's a recent sampling: In July a man walked into a law office in San Francisco with a gym bag full of guns and killed eight people before taking his own life. In October, a 19-year-old man opened fire at his health club in San Diego, killing four and then himself. The next day, a clerk at Fort Knox killed his boss and two co-workers before committing suicide, apparently because he didn't get a promotion. On November 1, a man entered a small town hall in New Hampshire with a shotgun and a pistol and shot anyone in his sight and then, when he ran out of targets, himself. Despite appearances, these are not what criminologists call ''murder-suicides,'' which are almost always family affairs and have not increased in frequency. Instead, they are mass murders that happen to end with the killer taking his own life. There is no separate statistic for this category, but it is ''definitely on the increase,'' according to Dr Kenneth Tardiff, a clinical psychiatrist at Cornell University. Besides the terrifying randomness of such attacks, one is also struck by their capriciousness. The discharged worker who 10 years ago might have cursed his boss under his breath today may be inclined to go home and get his gun. More people at the margin are using violence ''to make a statement,'' in Dr Tardiff's words. Murder as a means of self-expression. New York may not be the most violent city in America, but this year it leads the country in two especially chilling categories. Every day, on average, one person is killed by a stray bullet, i.e. a piece of hot lead hurtling randomly through space. You can't get more random than that. It's like being killed by a meteor or a bolt of lightning. The other category is taxi driver murders - almost one is murdered a week. Which brings us to the third ''R'': remorselessness. One robber, after he had collected his money, shot his victim in the head in front of four passengers - for no apparent reason- and then fled. Obviously he wasn't worried about witnesses. He just felt like killing someone. Then there was the young man who shot an obviously pregnant woman in the belly earlier this month even after she had given him her jewellery. Where are we when a young man - and there are dozens of similar examples - would just as soon kill someone as not?