The two contenders for the Democratic Party's presidential nomination have squared off in a spirited debate in New Hampshire.

The head-to-head between former Senator Bill Bradley and Vice-President Al Gore marks the beginning of a battle of style as much as substance.

The next three months will determine the first phase in one of the most important US presidential campaigns for more than a generation.

The primary contests of many of the key states have been grouped into the early part of the electoral cycle - known as "front-loading" in the jargon.

This means that, barring surprises, it should be clear by the end of March who will carry the Republican and Democratic banners into the final race for the White House.

In both camps an initial front-running candidate is being hard-pressed by a competitor who has turned the selection process into a real political battle.

The problems are perhaps greatest for the vice-president, who even jokingly tried to cast himself in Wednesday's debate as the outsider who would come from behind to win the New Hampshire primary on 1 February.

Mr Gore has good reason to worry. His opponent, the former basketball star and senator, is proving a highly effective candidate and is doing well in the only race that matters at the moment - raising campaign finance.

During the debate, while Mr Gore sought to stress his experience at the centre of government, Mr Bradley accused him of being "trapped in a Washington bunker".

This nicely sums up the chief difference between these two candidates: Mr Gore for better or worse is intimately associated with the Clinton administration; Mr Bradley claims to be peddling new ideas and a fresh start.

Healthy differences

Nowhere is this more true than in the field of health care.

Despite hi-tech medicine and medical research that is the envy of the world, the US is almost alone among affluent western countries in having no universal and comprehensive health care provision for all of its citizens.

Traditionally in the US, health care is funded by private insurance plans taken out by individuals or their employers, with certain categories of people assisted through government programmes.

At issue in this campaign is: Who should be helped by the government to buy insurance? What sort of level of support should be given? And who should pay for it?

Bill Bradley is proposing the more ambitious and more costly programme; one that would effectively offer financial subsidies for all working low-income Americans.

The availability of affordable private health insurance would be the main vehicle for extending health cover.

Mr Gore has a more modest and, he believes, more affordable proposal - targeting specific groups by expanding public health programmes.

Buried amidst the detail are two very different visions: Mr Bradley stressing equity and fairness; Mr Gore proposing more limited but achievable change.

Yet to ignite

But one of the paradoxes of this campaign is that no real issues have yet surfaced as decisive vote-winners.

The general level of affluence created by the long-running economic boom means that the campaign is yet to really ignite.

Given the compressed primary calendar, the danger is that each of the two parties may effectively have selected their candidates before America as a whole begins to grapple with the political agenda.

Mr Gore may be challenged by Mr Bradley but he still has strong support among key elements of the Democratic constituency, for example black voters.

Nonetheless he has an uphill task in New Hampshire - an atypical state true, but one which by virtue of being first in the nation to hold a primary could still give a huge boost to Bill Bradley's chances.