Republican presidential candidates George W. Bush and John McCain shadowed each other in New Hampshire today as though they were conducting two elections at once--first renewing their increasingly contentious primary battle over tax cuts, then joining forces to deliver a sharp attack on the military policies of their prospective Democratic opponents, Vice President Gore and former senator Bill Bradley.

McCain was especially aggressive in his remarks today, apparently confident that his intervention with a federal agency on behalf of a financial supporter was fading as a campaign issue. First the Arizona senator defended his tax cut plan as more conservative--and Republican--than Bush's, then he charged that Gore and Bradley had essentially disqualified themselves from the presidency because of their recently articulated positions on gays in the military.

At a news conference here following 30 minutes of questions from high school and college students at a "Presidential Candidates Youth Forum," the Arizona Republican defended his tax cut plan as more "conservative" and "Republican" than the larger tax cuts advocated by Bush because it would provide more money to shore up the Social Security system and pay down the national debt.

"I think most Americans and conservatives think that low- and moderate-income Americans need a tax break the most," he said. "I think most conservatives believe we have an obligation to pay down the national debt."

Bush, who arrived in New Hampshire late this afternoon, gladly took up the tax fight, saying he enjoyed having a debate with McCain over tax policy, a subject on which he said they have "a fundamental disagreement." Bush has called for a far broader tax cut, giving a break to the rich as well as the poor, in which the highest tax bracket would be lowered to 33 percent. The lowest bracket in his plan would drop from 15 percent to 10 percent. He would use most of the projected budget surplus to fund his tax cut.

When asked about McCain's recent claim that Bush's plan to use the surplus for such a massive tax cut was unwise, Bush responded: "I believe it is unwise to leave unspent money in Washington. It leads to bigger government."

Tonight, Bush, McCain and the four other GOP candidates--publisher Steve Forbes, conservative activist Gary Bauer, radio talk show host Alan Keyes and Utah Sen. Orrin G. Hatch--each addressed a state party dinner at which McCain said Gore and Bradley were "not qualified" to be commander in chief of the armed forces.

Citing debate statements by Gore and Bradley that they would insist that the next chairman of the Joint Chiefs of Staff allow gays to serve openly in the military, McCain accused the Democrats of seeking to "impose a social agenda" on the military and that this alone disqualified them to be commander in chief. Gore said during a debate last week that he would make this a litmus test in naming a Joint Chiefs chairman, but he quickly reversed that position, saying he would not delve into the personal views of an appointee to that post.

Despite Gore's reversal, the Republican National Committee said it intends to follow through with plans for a new TV ad accusing Gore of advocating a policy that would prohibit the popular retired generals Colin L. Powell and Norman Schwarzkopf, who commanded allied troops in the Persian Gulf War, from serving on the Joint Staff.

RNC spokesman Mark Pfeifle told the Associated Press that it's fair to air an ad based on Gore's original comments because "words matter." Gore's "inability to communicate in a clear and concise matter is a very viable political issue," he said, because any president must negotiate with foreign leaders and address the American people.

In response to McCain's comments, Bradley spokeswoman Anita Dunn repeated that Bradley will have no such litmus test for the chairman of the Joint Chiefs of Staff. "Senator McCain's statement has more to do with Republican politics than with candidate qualification," she said.

McCain returned to this first-in-the-nation primary state the day after his aides released more than 500 letters he has written to federal agencies on behalf of various companies and individuals, some of whom have contributed to his campaigns and some who have not. The deluge of paper was meant to blunt a controversy over a letter McCain wrote to the Federal Communications Commission last year urging a decision on a television station acquisition application by Paxson Communications, a firm whose executives have contributed to his campaign and provided company aircraft for his use.

The issue threatened to undermine McCain's image as a "maverick" who has made cleaning up the campaign financing system the centerpiece of his presidential campaign. But McCain and his aides were encouraged by the apparently dwindling interest in the issue here today, where there were no questions on the FCC matter at the youth forum and only one from reporters at the news conference.

Asked whether he thought Bush operatives were responsible for the FCC letter becoming public, McCain said, "It doesn't matter. This campaign is very tough and it's getting more intense. The worst thing you can do is to get diverted by something like this, which causes you to get off your game."

"The FCC [controversy] is gone," a McCain aide said after the news conference.

Aboard his campaign bus on the way to a state GOP dinner in Durham tonight, McCain was less willing to declare the FCC letter episode over. "You never know because you can't control it," he said. "But the tactic that works best is to get all of the information as you can out."

To that end, he said on CBS's "Face the Nation" that he is asking all federal agencies to release any correspondence from him. A campaign spokesman said that instead of the senator simply making the request, the Senate Commerce Committee would seek the documents under the Freedom of Information Act.

Reiterating his argument that as Commerce Committee chairman he has an obligation to urge action, but not specific outcomes, by agencies under the panel's jurisdiction, McCain said, "What I hope people would say is, 'Here's a guy who's doing his job.' "

McCain sidestepped questions about whether he was even aware of the content of many of the letters that went out under his signature. "It's my responsibility," he said. "I'm kept well-informed. It certainly isn't a staff person of mine who is responsible."

The issue of exerting senatorial influence, however, is spreading to other campaigns. Bradley, who has joined McCain to promote overhauling campaign finance laws, said in Iowa today that while he "had a practice of not intervening in regulatory matters," he invited reporters to "go take a look" at his Senate correspondence, archived at Princeton.

McCain is scheduled to unveil the details of his tax plan Tuesday in the New Hampshire capital of Concord. "My plan is more responsible [than Bush's] because it does not assume that the surplus will be there forever," he said. "To bank it [tax cuts] all on the surplus at the possible risk to Social Security is our fundamental difference."

McCain, who has accused Bush of tilting his tax plan to benefit wealthy Americans more than others, emphasized that his tax cuts would be aimed at low- and middle-income taxpayers. "They need it," he said. "I'm not sure that very wealthy Americans need it."

Staff writer Mike Allen in Iowa contributed to this report.

CAPTION: Sen. John McCain (R-Ariz.), above, and Texas Gov. George W. Bush answer questions at a "Presidential Candidates Youth Forum" at Saint Anselm College in Manchester, N.H. Later, McCain said Democrats Al Gore and Bill Bradley were "not qualified" to be commander in chief of the armed forces.