With temperatures rising between Texas Gov. George W. Bush and Arizona Sen. John McCain, the field of Republican presidential candidates returns to the debate stage tonight in New Hampshire.

Bush and McCain have sparred this week over tax cuts and campaign finance reform. Their running argument over the size and scope of their respective tax plans signals the intensifying competition between the two men, particularly in New Hampshire, which holds the nation's first primary on Feb. 1.

McCain now leads Bush in the New Hampshire polls, and Bush has noticeably stepped up his campaign activity here -- hoping that a victory in New Hampshire will cripple McCain's candidacy. But Bush is attempting to overcome doubts about his own candidacy raised by earlier debate performances and criticism that he has not campaigned hard enough in New Hampshire.

McCain arrives for tonight's debate on the defensive over reports of his intervention with the Federal Communications Commission in a case involving a campaign contributor who is trying to buy a Pittsburgh television station. McCain did not ask the FCC to rule in favor of Paxson Communications and said he was only trying to prod an unresponsive bureaucracy to make a decision after two years of delay.

But the case has raised tough questions for a candidate who has made cleaning up the campaign finance system and taking power away from moneyed interests in Washington the central theme of his presidential campaign.

McCain on Wednesday urged all candidates to "lead by example" in helping to restore public faith in the public process, but spent much of the day answering questions about the FCC matter.

Tonights' debate, the first of three that the Republicans will hold between now and Monday, will air at 7 p.m. on MSNBC and C-SPAN and will run for 60 minutes. Most of the attention will be on Bush and McCain, but the four other GOP candidates need to use tonight's debate to boost their campaigns as well.

In previous debates, Steve Forbes, Gary Bauer, Alan Keyes and Utah Sen. Orrin G. Hatch have drawn generally good reviews, but they are still struggling to attract more attention and voter interest.

This morning Bush campaigned in Salem and when asked about what sets him apart from McCain told a business audience "I have been in a chief executive's role before. I have led." Bush also said he and McCain differ on how they would attempt to clean up the problem of unlimited soft money contributions in American politics. Bush said he would protect Republican and conservative interests and said McCain would not.

As he does virtually every morning in New Hampshire, McCain began the day with a town meeting. As he boarded his campaign bus to head to the event, he he happily told reporters: "I've got my lucky shoes on!" He hiked his trouser cuffs to reveal a clunky pair of waffle-soled walking shoes. "L.L. Bean! I wore them in the first debate and now I have to wear them every time."

Reporters on his bus were probing, for the second day running, the reasons why the champion of campaign finance reform would write a letter to a federal agency on behalf of a big campaign contributor. But the several hundred citizens gathered at the fire station in Bow had their own concerns, ranging from veterans' benefits to cold fusion.

McCain opened the meeting by criticizing a decision by immigration officials to return a 6-year-old Cuban boy to his father on the communist-run island. "The only people who have been sent back to Cuba in the past are criminals," McCain complained. "I think the president of the United States ought to exercise some leadership and allow this young man to remain."

He also made a pitch for his tax-cutting philosophy, which is much more reserved than Bush's. Taxes "are emerging as an issue in this campaign," he told his audience, and his renewed his charge that Bush plans to cut too much-especially for the wealthy.

"I don't think rich Americans right now need tax breaks," McCain said to scattered applause. "We ought to pay down the debt."

The senator visited another fire station for lunch, then spent the afternoon preparing for the debate.