The first nine months of the Republican nomination fight were mostly about a political phenomenon called George W. Bush: his money, his endorsements, his big lead in the polls. The last five weeks have belonged more to Arizona Sen. John McCain. Suddenly the Texas governor appears to have a race on his hands.

The campaign of 2000 continues to surprise. Operating on a timetable never before seen, the Republican race already has taken on the shape of a contest that usually occurs after the Iowa caucuses and the New Hampshire primary. In a race in which the voters have yet to be heard from, the once-large field has been cut in half and McCain has emerged as the principal alternative to Bush.

"This is a much more mature race much earlier than I've ever seen it," said Tom Rath, the New Hampshire Republican national committeeman and a Bush adviser. "We've had a virtual primary on the basis of polling data."

Bush allowed McCain an opening in New Hampshire, and the Arizona senator seized it. "At some point we all knew there would be an alternative, and I think we [have] arrived at that point now with McCain," said Kyle McSlarrow, who managed former vice president Dan Quayle's campaign. "I think it's a real thing."

McCain's rise--notable mostly in New Hampshire--has its roots in a variety of developments. They include the early departures of such candidates as Quayle, Lamar Alexander and Elizabeth Dole. They also include the failure of wealthy magazine publisher Steve Forbes to consolidate the conservative wing of the party, as he has long predicted he would do.

But the McCain rise owes to other factors as well: a best-selling memoir of his days in a North Vietnamese prison camp; a maverick's appeal to independents and voters disenchanted with the system; a direct style in a year when "authenticity" has become a buzzword for what voters want; Bush's decision to skip two recent candidate forums in New Hampshire; and questions about whether Bush's candidacy is grounded in more than a claim that he can win.

Three other Republicans remain in the race: Utah Sen. Orrin G. Hatch, former Reagan administration official Gary Bauer and former ambassador Alan Keyes. But attention is fixed on the Bush-McCain dynamic. "The question is whether McCain can grow outside of New Hampshire and sustain what he's got going in New Hampshire," said GOP strategist Don Sipple.

Having broken away from the rest of the pack of candidates chasing Bush, McCain faces fresh challenges. He remains underfunded compared with the massive campaign war chests of Bush and Forbes. The only states where he has a campaign organization are New Hampshire, South Carolina and Arizona. And questions about whether he has the temperament to be president represent only the first round of intensified scrutiny that will come at an accelerating pace.

For most of the summer, the focus of the Republican race was on Iowa and the state GOP's Aug. 14 straw poll, won by Bush, but not by an overwhelming margin, with Forbes second. Since then, the focus has been on New Hampshire, where the race has tightened significantly.

Where it was once Bush against the field in New Hampshire, it is now simply Bush vs. McCain, with the senator climbing to within 10 points in one poll released this week. Two months ago, that same poll showed Bush with a lead almost four times as large. The poll even showed McCain running better than Bush against Vice President Gore and Bill Bradley in the state.

The size of the sample in the most recent poll, conducted by Franklin Pierce College for WNDS-TV, is small enough to raise questions about just how big the margin is between Bush and McCain. But other polls the past few weeks also have shown McCain's support against Bush steadily increasing.

Rath called McCain's emergence the result of "gravity as opposed to momentum"--built more on the disappearance of others from the race than on solid support for McCain. He said McCain may have trouble enlarging or even sustaining his support in New Hampshire, given the amount of time until the Feb. 1 primary.

McCain advisers say those are welcome problems compared with obscurity and single digits in the polls. "It's even better than we would have hoped," pollster Bill McInturff, a McCain adviser, said of his candidate's emergence. "And I can guarantee the Bush people didn't expect it happen."

The Bush camp denies that's the case, sort of, but for months they anticipated and planned for a negative media war with Forbes. Instead they face McCain, a military hero with strong foreign policy experience--in contrast to Bush, who had trouble identifying the leaders of four nations this week--and a candidate who, like Bush, has pledged to run a positive campaign.

McCain advisers say their candidate's rise puts pressure on Bush to adapt his campaign for a different kind of race. "It's not what we're going to do, it's what they're going to do," one McCain adviser said. But he added, "We had a plan, but it was a plan that called for this to happen on January 15. We'll have to show a little more strategic flexibility."

McCain's route to the nomination is clear, though not easy. He hopes to win in either New Hampshire or South Carolina and in his home state of Arizona and build from there--with major emphasis on the March 7 California primary, which is likely to settle the nomination.

"There's no question that it all boils down to New Hampshire and South Carolina, and if John McCain wins in either state it sends shock waves through the party and it's a whole new ballgame," said Whit Ayres, a Republican pollster who worked for Alexander's 1996 campaign. "The odds favor Governor Bush winning because of his financial advantage, but it no longer is an easy coast to the nomination."

McCain has chosen not to compete in the Jan. 24 Iowa caucuses, where Forbes is working hard, although he has begun to waver on that decision since Dole dropped out. McCain's strategy is risky but perhaps the only one available to a candidate with limited resources.

"If we've done well in New Hampshire and won South Carolina and Arizona and are competitive in Michigan and Virginia and Washington, then California is entirely winnable," said Rick Davis, McCain's campaign manager.

Bush's route is equally clear: Compete to win in every state but be strong and deep enough to sustain one early defeat. Bush has built campaign organizations in all 50 states and has a game plan that calls for heavy television advertising in every media market in each of the important early primary and caucus states, as well as in California.

"The race is different in that other people got out sooner than we thought and McCain had the luxury of being able to focus all his time and resources on New Hampshire," one Bush adviser said. "But the basic thesis, that we were running with the only national candidate, . . . has not really changed."

Bush advisers argued that McCain may be doing well in New Hampshire but that he does not have the resources or the appeal to compete on equal footing after that. "Here's a guy who's only been able to move numbers in one state by spending enormous time and effort in that one state," a senior Bush adviser said. "That's a smart move, but it's not a sign of long-term strength."

The biggest wild card in the GOP race is Forbes, whose huge bank account has done little to boost the candidate out of single digits. Forbes advisers said in June that they were launching a $10 million summer advertising blitz. Bush and McCain supporters, who closely track the media buys of their rivals, claim Forbes spent far less--about $3.5 million.

For the past two months, the Bush campaign has watched with growing puzzlement--and clear relief--as each week passed without Forbes launching a new round of advertising. "I think he's waiting way too long already," a Bush adviser said. "The time to do it was when we weren't on the air." Now Forbes's rivals question whether the self-financed candidate will dip into his family fortune to fund the kind of advertising barrage long anticipated.

"Let them run their campaign; we'll run ours," a Forbes adviser said.

Forbes has said he will launch new ads before Thanksgiving, but his opponents argue that he runs the risk of hurting himself if those ads are perceived by voters as negative. Republican strategists argue that since Forbes's summer advertising campaign did little to boost his standing, he has checkmated himself because of the kind of negative campaign ads he ran four years ago.

Still, with McCain not running hard in Iowa, Forbes has an opportunity to challenge Bush there. Forbes spent several days in Iowa this week and drew sizable crowds. His advisers say the crowds signal a strong grass-roots organization that they have replicated in other states. That, they argue, means they will have more capacity to compete against Bush beyond the first few states.

"We've built a phenomenal grass-roots organization in all the key states," a Forbes adviser said. "We'll use electronic and print media when appropriate and where appropriate and hit them when they won't have time to recover."

Curiously, McCain may need Forbes's help to defeat Bush in New Hampshire, with Forbes taking conservatives away from Bush and McCain challenging the front-runner for moderates and independents. "Forbes can make it substantially easier for McCain to win if he takes any significant chunk of the conservative vote in New Hampshire," pollster Ayres said. "But if he decides to beat up on Governor Bush, . . . his own negatives are going to go through the roof."

Forbes still counts on becoming the candidate on the right, but he must worry about Bauer and Keyes, who are appealing to social and religious conservatives. Even more of a problem is that Bush enjoys considerable support on the right himself.

"I think what conservatives have shown this year is that for whatever reason they have refused to coalesce around one candidate," McSlarrow said. "It wasn't us, it isn't Bauer, it hasn't been Forbes. Bush's numbers would not be where they were without some significant portion of the conservative electorate."

That represents one of McCain's hurdles as he thinks about how to build on his strength in New Hampshire. The New Hampshire electorate is unique. Among the early primary and caucus states, it has the lowest proportion of voters who call themselves "very conservative."

"His instincts are to run left," said a GOP strategist who worked for Robert J. Dole's 1996 campaign. "That is what's gotten him this tremendous press and the huge boost in the polls. But in January it's the primary voters who matter, and they will want to hear a conservative message. That's McCain's real challenge."

But for now, McCain's emergence in New Hampshire has presented Bush with the first serious challenge of the campaign. For all the confidence Bush and his advisers exude, they know they have a difficult race and that McCain is a credible rival, and his rise has shaken up their New Hampshire operation.

"If there's any concern we had about our team in New Hampshire," a Bush adviser said, "there's no complacency now."