BALTIMORE, Md. (AP) _ New Hampshire primary winner Paul Tsongas pronounced himself and Arkansas Gov. Bill Clinton front runners in the Democratic presidential race today and said they would soon go ''head to head on economics '' in a nationwide campaign for the nomination.

Tsongas savored his up-from-nowhere victory in the inaugural primary. Asked by a reporter if he felt like a heavyweight, he struck a prizefighter's pose with clenched fists held aloft. A charted Carnival Airlines 727 jet bore testament to his suddenly heightened political prospects.

Aides laid out a hectic schedule throughout several states over the next few days and said Tsongas would plant his flag in all regions of the country as well as replenish his campaign coffers.

The former Massachusetts senator rejected concerns about his ability to compete outside his native New England, and scoffed at suggestions that a prominent Democrat could make a late, successful entry into the race.

''Let 'em come in. Let 'em come out and compete,'' he said before departing New Hampshire. ''We'll take 'em on, We'll beat 'em.''

Tsongas said Maryland's March 3 primary ''is our main battleground'' in the next round of contests with Clinton. He paid his rival a compliment, saying he had a more thoughtful economic program than the other Democrats in the race, Nebraska Sen. Bob Kerrey, Iowa Sen. Tom Harkin and former California Gov. Jerry Brown.

Then, he swiftly ticked off several areas of disagreement.

Clinton favors a tax cut for the middle class, which Tsongas opposes. Clinton favors expanded tax breaks for having children, which Tsongas also opposes. He also expressed concern about the cost of various Clinton-backed programs and said his rival has no plans for controlling the deficit.

In general, Tsongas favors using tax incentives to rebuild America's manufacturing industries, including a cut in the capital gains tax, backing for research and development and business formation.

He blends his pro-business approach with a liberal social agenda, and said he compares favorably with Clinton on abortion rights, environmental protection and gay rights.

He sidestepped questions about Clinton's alleged womanizing and draft- dodging. Asked about the so-called character issue, he said, ''nobody's perfect.''

But at the same time, he said Clinton's unfavorable ratings in polls in several states are higher than his own. ''I have great potential to move,'' he said.

Even before the votes were tallied, the 51-year-old Tsongas mapped a seven- state sprint over four days - Maine, South Dakota, Maryland, Georgia, South Carolina, New York and Massachusetts - designed to plant his front-runner's flag for the upcoming primaries and replenish his warchest.

Clinton, meanwhile, told supporters at a final New Hampshire rally he was ''convinced that once the people hear this message all over the country, that we're going to win the nomination and go on to a great victory in November.''

''Last night's results plainly show in both parties that the people wanted change in the business-as-usual politics of Washington, and that's what we stand for,'' Clinton said before leaving for Georgia.

The next all-out collision for Tsongas and Clinton shaped up as the Maryland primary on March 3.

Nebraska Sen. Bob Kerrey, Iowa Sen. Tom Harkin and former California Gov. Jerry Brown Jr., trailed in the New Hampshire balloting and all vowed to persevere. Nearly a third of voters told pollsters they wished some other candidate had been on the ballot, but write-in efforts for Mario Cuomo and Ralph Nader gained only 3 percent and 2 percent, respectively.

At an airport news conference before leaving New Hampshire, Kerrey told reporters he had questions about Tsongas' qualifications for president. ''I love the guy, I'm a great fan of his, but he's a corporate lawyer and a lobbyist,'' Kerrey said.

Tsongas reveled in his victory.

Interrupted by a ringing telephone, he quipped: ''Answer the phone and tell George Bush he cannot concede til November.''

He stressed his anti-establishment candidacy, saying he was offended by the ''arrogance'' of party leaders talking of enticing a late entry into the race. Democratic congressional leaders have made no secret of their distaste for Tsongas' views and their concern about his nationwide appeal.

He underscored opposition to the middle-class tax cut that congressional Democrats, Clinton and others favor.

''We don't want giveaways, Washington. We want an economic battle plan,'' said the man who has distributed thousands of copies of his 86-page economic treatise to New Hampshire voters.

He wants money to go to tax incentives and investments that will create jobs, and told an ABC-TV interviewer, ''We're going to find out in the next several states which of these visions has appeal.''

Tsongas also said he is prepared for a fresh round of questions about his three-year battle with cancer. ''That's going to be an issue. ... I have to reassure people,'' he said. To do that, he is airing television commercials in upcoming primary states with a New Hampshire-tested ad showing him swimming.

Tsongas was diagnosed with lymphoma in 1983, and underwent a bone marrow transplant and radiation as part of his treatment. His doctors have given him a clean bill of health for his campaign.