Jen O'Malley wasn't looking for trouble. She had come to the Democratic presidential debate here last month to cheer for her man, Al Gore, and to wave a "Gore 2000" sign in front of the TV cameras. But suddenly, things turned ugly.

A pack of Bill Bradley supporters, intent on waving their signs for the cameras, knocked O'Malley to the ground, injuring her knee. Fearing a trampling, she curled up in the fetal position, enduring a kick in the back before being rescued by police. "I came to the debate to show my support--I had no idea I'd end up at the bottom of the mosh pit," says O'Malley, Gore's volunteer coordinator in Manchester. "Those Bradley kids are tough."

When it comes to hooliganism, the Gore partisans are no slouches, either. The same night, Bradley's New Hampshire spokesman Mo Elleithee attests, a Gore partisan pushed a Bradley staffer in front of a moving minivan.

The police, who once again intervened, are as baffled as anybody by the fisticuffs. "I expected more of a Grey Poupon crowd," says Sgt. Tim Goulden, a station supervisor for the Nashua police. "These are two of the mellowest candidates in the world."

Not anymore. In recent weeks, the Democrats' campaigns have picketed and disrupted each other's events. Gore folks have assigned a six-foot ear of corn to "stalk" Bradley when the New Jerseyan comes to Iowa; earlier, the Gore campaign sent a human chicken to a Bradley fund-raiser in New York (demonstrating Bradley's alleged fear of debates) and dispatched senior citizens--"our Gray Panthers," says a Gore spokesman--to do jumping jacks at a Bradley event in Iowa (mocking his idea that exercise would cut Medicare costs). Bradley isn't innocent, either: A Bradley disruption outside Gore headquarters in Nashua prompted a call to the authorities.

Presidential politics has always been a nasty business, of course. But while the trend on the Republican side has been toward cordiality--Steve Forbes, the tiger of '96, is more of a pussycat this time--Democratic rudeness seems to have escalated. Ray Buckley, the deputy Democratic leader of the New Hampshire House, told the Manchester Union Leader that protests by Bradley supporters at a Gore event with Gov. Jeanne Shaheen descended to a level not seen even in the McGovern-Muskie or Carter-Kennedy battles. "What were they so angry about?" Buckley wanted to know.

What, indeed? Let's put the question to John Rauh, one of Bradley's top activists in New Hampshire. "It's the childishness, the lack of respect," he says. The vice president of the United States is "immature, rude and not telling it like it is." Still, Rauh's disgust has its bounds. After much prodding, the Bradley man confesses he'll back Gore, rudeness and all, if he wins the nomination.

Therein lies the strangest element of the Democratic fight. With few exceptions, there is little history of bad blood between the Gore and Bradley operatives. They've spent years working on the same side of campaigns, and many of them are pals. Anita Dunn, Bradley's communications director, is a business partner of Bill Knapp, a Gore strategist. Knapp, in turn, counts among his best buddies Mark Longabaugh, Bradley's New Hampshire director.

David Ginsberg, Gore's research director, is thick as thieves with Bradley's researchers. Michael Whouley, a top Gore tactician, has fought side by side with Longabaugh, and Gina Glantz, Bradley's campaign manager, goes all the way back to the Mondale campaign with her friend Donna Brazile, Gore's manager. Matt Henshon, Bradley's special assistant, believes his law-school pal Chris Lehane went to work as Gore's campaign spokesman because "he's trying to make up for all those times I beat him in intramural basketball."

Even while the insults and accusations fly, the two sides can't help but fraternize. In December, the New Hampshire staffs for the two campaigns got together for their second basketball competition (the Bradley forces won, of course). "We'll all be friends again in April," Ginsberg says.

And why shouldn't they get along? Their bosses are fairly similar: both mushy moderates at heart, and both by necessity playing to the party's liberal base. They're not split over life-and-death issues such as abortion. Instead, Gore and Bradley are hurling invectives over the intricacies of health-care policy.

Some of the combatants realize that the intensity of their spat is farcical. "It's really not about the issues," says Russ Nadler, a 22-year-old volunteer troublemaker for Gore. "We've got two centrist, free-trading Democrats." But that doesn't stop Nadler from driving to a Bradley appearance at a shopping mall in Nashua, his pickup truck carrying Gore placards and a sound system--tools of disruption. When Bradley arrives, Nadler's gang waves Gore signs and chants "Gore! Gore! Gore!" until a security guard informs them: "This is a shopping mall. Please behave yourselves."

Back in his pickup, Nadler says the heckling is retaliatory: Bradley, Nadler insists, is the one who made this campaign nasty. "They show up at all our events," he complains.

True enough, admits Longabaugh, Bradley's man in New Hampshire. The very morning of the mall attack on Bradley, Bradley partisans showed up at Gore's hotel to abuse the candidate when he went for a jog. But Longabaugh insists it's Gore who started the nastiness. "I don't see how you could have any other interpretation," he says. "They panicked, and Al Gore started attacking us."

It was not always like this. For most of '99, Gore's strategy was to ignore Bradley, and Bradley spent his days talking about "big ideas," making only implicit reference to Gore. But that changed in the fall, when Bradley passed Gore in the New Hampshire polls and Gore began to tell America that Bradley's health care plan would bust the budget surplus, wound the elderly and infirm, and bring about disaster generally. The Bradley campaign largely ignored the assault--until early December, when Bradley partisans released their pent-up anger.

Longabaugh, who had unsuccessfully been urging Bradley headquarters in New Jersey to take a tougher position against Gore, sent out a letter calling the vice president "disingenuous" and "cynical" and said the Gore campaign was guilty of "utter fabrication of the facts, and the vice president knows it." A couple of days later, Bradley loyalists were handing out fliers at New Hampshire pharmacies accusing Gore of "uncontrollable lying." The Bradley campaign apologized.

Since then, the campaigns have deteriorated into a so's-your-old-man volley of accusations. Bradley gives a speech declaring that during his presidential announcement, "Al Gore spoke 2,836 words, but never were the three words 'campaign finance reform' mentioned." Gore forces retaliate with their own number: "Bradley waited 6,219 days after joining the Senate to author a campaign finance reform bill."

Pettiness is no obstacle. Gore puts out a press release to say "New Jersey's Frank Lautenberg Endorses Gore." Bradley responds with a statement titled: "Senator Frank Lautenberg Already Endorsed Gore." Bradley puts out a partial transcript of an NBC report about Gore's "distortions." Gore responds by releasing a fuller transcript of the report, which includes the line "Bradley has gotten it wrong too." At the New Hampshire debate, Gore forces fire off four "Reality Checks" of Bradley statements, and Bradley forces counter with three of their own reality checks, including a reality check of a Gore reality check.

A few days later, Bradley has moved on to attack Gore about agriculture policy. While Iowa farmers suffer, he says, "after seven years, the vice president has offered nothing more than negative attacks and distortions."

Precisely three hours and 11 minutes later, Gore forces in Iowa announce that they are about to unveil "Corn Man," a six-foot-tall, human ear of corn. Corn Man will be "stalking" Bradley at his Iowa appearances to give the candidate an "earful" about Bradley's unwillingness to debate. "There's a farm crisis going on, and it's shameful that Bradley won't even let Iowans know where he stands," Corn Man says in a prepared statement.

It was perhaps inevitable: In this nasty campaign, even the vegetables have become rude.

CAPTION: The Gore campaign's "Corn Man" shows up at a Bill Bradley appearance in Des Moines last month to spotlight Bradley's unwillingness to debate there.