WASHINGTON -- One year after President Bush launched an air war in the Persian Gulf, the Democrats who want his job have opened a massive aerial campaign of their own.

This time, the combat zone is the frigid sky over northern New England, the targets are Americans -- specifically, 100,000 or so New Hampshire voters -- and TV commercials are the weapons.

With primary and caucus season just three weeks away and the Democratic hopefuls still a mystery to voters, paid advertising will be more important than ever this year. The throw-weight of the New Hampshire ad blitz testifies to the enormous stakes in next month's primary election there.

"Each candidate will spend more in four weeks than McDonald's is going to spend in a year" on New Hampshire advertising, said Carter Eskew, a media adviser to Iowa Sen. Tom Harkin's presidential campaign. During the first week, for example, the average Granite State TV viewer is expected to see Harkin ads at least 12 times.

It is doubtful that any of the major contenders can survive a poor showing in '92's first primary, because campaign contributions, already in short supply, would quickly dry up. Also, the current, early favorite is a Southerner, Gov. Bill Clinton of Arkansas, who could be very hard to stop if he scores a victory in New Hampshire, just before the campaign moves south for a big round of primaries in March.

This year's Democratic air war, like the campaign itself, which started late with an obscure cast of candidates, is breaking the mold of presidential politics.

Against a backdrop of economic chaos in New Hampshire, where angry voters are demanding solutions, all the contenders are attempting to project an image of seriousness. Mr. Clinton, Mr. Harkin and Nebraska Sen. Bob Kerrey began beaming their first 30- and 60-second ads last week, and all sought to grab a specific issue, such as the economy, trade or national health insurance.

None of the three opened in the conventional way: with a biographical ad introducing himself to the voters, even though polls confirm that, as in other states, most voters in New Hampshire know little or nothing about the candidates. (The other major contender in the primary, former Massachusetts Sen. Paul E. Tsongas, ran his first ad last fall. Regarded as a poor television performer, he is the only candidate who does not speak in his own ads.)

Their media advisers say the candidates are taking a fresh approach this time because of the unusual circumstances of the campaign, namely, the rotten economy and widespread disgust with traditional politics and politicians.

"People are so frustrated they want to know less about who you are than what you want to do," said David Axelrod, a Clinton adviser.

Mr. Kerrey and Mr. Harkin apparently rushed to get ads on the air to match Mr. Clinton's, and some campaign aides attributed their issue-oriented approach to a desire to latch on to substance from the beginning to prevent Mr. Clinton from appearing to be the candidate with all the answers.

At least one media consultant, speaking from experience, thinks the Democrats are making "a dreadful error."

Raymond D. Strother, who devised the commercials for Gary Hart's 1984 campaign, says that until the voters get to know them, "there will always be a danger for these candidates to rise quickly and fall quickly."

Eight years ago, Mr. Hart came from nowhere to upset Walter F. Mondale in New Hampshire. But because his campaign had failed to introduce him properly, he went down nearly as fast, once Mr. Mondale began attacking his supposed lack of substance.

Presidential campaign aides concede that any candidate who does not define himself risks being defined by an opponent in a damaging way. ("On the other hand, not everybody's as weird as Gary Hart," one adviser adds.)

Campaign aides say the opening volley of ads is part of the process of defining the candidates, despite the untraditional approach.

Mr. Clinton's first ad, showing him seated in the governor's office, surrounded by American flags, "is an introductory spot simply because he's there," agreed Douglas Bailey, a Republican media consultant and publisher of the Hotline, a political news service. "It's more powerful than a bio spot [because] Bill Clinton projects a powerful and presidential image."

In his commercial, Mr. Clinton sympathizes with New Hampshire's economic troubles and invites viewers to call for a free copy of his 44-page "Plan for America's Future." The booklet, printed on un-slick paper, is his answer to Mr. Tsongas' 83-page pamphlet, which has attracted considerable attention from serious-minded New Hampshire voters.

Perhaps the most talked-about ad, at least in campaign circles, is Mr. Kerrey's hockey spot, which attempts to connect with the local sports mania. Dressed in a business suit, the candidate leans against a hockey net and talks tough about the need to defend America against unfair Japanese trade practices.

The Kerrey commercial has drawn comparisons to one of the most decisive ads of the 1988 presidential campaign, Richard A. Gephardt's "Hyundai" spot, credited with sparking his victory in the Iowa caucuses. Robert Shrum, the Kerrey campaign's media consultant, also created that ad.

Without TV advertising, a Kerrey adviser contends, none of the other candidates would have a chance to stop Mr. Clinton from winning New Hampshire and possibly wrapping up the nomination in the weeks that follow. A recent New Hampshire poll showed Mr. Clinton leaping into first place in the Democratic contest after several weeks of favorable press attention.

"The media has sort of anointed the guy," complained the Kerrey adviser. "If you didn't have paid media, the whole thing would be sort of hopeless."

Absent some well-known candidate in the field, the race has begun to revolve around the campaign commercials.

Hardly a day goes by without one candidate attacking another over a statement or claim made in a TV ad. On Friday, for example, the Kerrey campaign hit back at a new Clinton commercial that criticizes "Washington politicians" who voted for the congressional pay raise (both Mr. Harkin and Mr. Kerrey did).

"Governor Clinton has been running with virtually no scrutiny of his record. The voters of New Hampshire know very little about Governor Clinton except the slick ads and long rhetoric," protested Paul Johnson, the Kerrey campaign manager in the state, in a statement. However, the Kerrey campaign apparently failed to do any research of its own; if it had, it could have debunked Mr. Clinton's ad claim that he "never had a pay raise" in 11 years as governor by pointing out that the Arkansas Constitution bars raises for sitting governors.

All the major candidates are hoping to keep their ads on the air from now until the election, a further indication that media politics has arrived in a state that still clings to the ideal of one-on-one campaigning. Indeed, until the 1980s, television advertising wasn't even used in the New Hampshire primary, because campaign strategists felt it was too expensive for such a tiny electorate.