As the six Republicans line up for their presidential nomination race, they all know that unless George Bush clips a hurdle in the early stages, no one is likely to catch him.

Each of the five other runners -- from established challengers Bob Dole and Jack Kemp to such untested opponents as Pete du Pont, Al Haig and Pat Robertson -- has his own strategy for winning the race.

But they recognize that the spotlight is on the man with all the advantages, the man with No. 2 stenciled on his well-tailored warm-up jacket.

That's the bad news. The good news, they think, is that the hurdles are higher in Bush's lane and that there are hidden potholes in his path. Some of the barriers are the early-voting states: Iowa, where Bush is a step behind Dole in the latest poll, Hawaii, Michigan, Minnesota, New Hampshire and South Dakota.

But the trickiest hurdles for Bush may be the televised debates, starting late next month. That's where long shots Pierre S. (Pete) du Pont IV, the former Delaware governor, and Alexander M. Haig Jr., the former secretary of state and White House chief of staff, who clearly cannot match the others in money or organization, really hope to make their presence felt.

During the summer months, while Vice President Bush has been relatively idle, Sen. Robert J. Dole (Kan.) and Rep. Jack Kemp (N.Y.) have been recruiting and organizing at a frantic pace. They appear ready for the test. Television broadcaster-evangelist Marion G. (Pat) Robertson's followers have been turning up the heat on his petition drive in anticipation of the Sept. 17 deadline for the 3 million signatures he set as his target a year ago.

But "the race can't begin until Bush gets in," as Dole's chairman, Robert F. Ellsworth, concedes. And that is still six weeks away.

A canvass of opinion in the rival camps and among neutral GOP observers shows that Bush's advantages are enormous. "Bush has one hell of a lead," says Richard S. Williamson, a veteran GOP operative until recently aiding former senator Paul Laxalt of Nevada, who last month quit the race. "He's used his advantages effectively and he has not made mistakes."

Bush had raised more than $9.4 million by the start of the summer, more than twice as much as his closest competitors, Dole and Kemp. Bush has far more endorsements of elected and party officials than anyone else, including more House members from New York than are backing their colleague from Buffalo, Kemp. "The head tables are his," Dole tells audiences. Bush also has the deepest, broadest organization -- the only one, a senior GOP official says, "really prepared to compete everywhere."

Most important, Bush has seven years as Ronald Reagan's chosen lieutenant in two campaigns and two administrations, with a reputation for unblemished loyalty that none of his opponents dares to question. "In the eyes of a great many Republicans," says a GOP governor who looked at the race and decided not to get in, "George has earned the nomination already."

That "deference factor" is particularly strong in the southern states, where the existing Republican Party is largely a creation of the Reagan-Bush years. At opposite ends of the South, Bush is solidly anchored in his adopted state of Texas and in Florida, where Gov. Bob Martinez leads an overwhelmingly pro-Bush GOP establishment. A Scripps-Howard News Service poll of 14 southern and border states, released over the weekend, shows Bush with a commanding lead in the South -- the first choice of 48 percent of those who said they planned to vote in GOP primaries. Dole was listed as first choice by 20 percent and Kemp by 6 percent in the poll of 1,061 potential voters.

It is in the South that Bush's manager, South Carolinian Lee Atwater, believes Bush can recoup from any early stumbles. The southern "Super Tuesday" primaries March 8 represent Bush's safety net. In theory.

In fact, by that point, Bush and the others will be involved in a national campaign, dominated by national news media, and there is no way to isolate voters in one section of the country. "If Bush is in free fall after New Hampshire," says John Buckley, Kemp's campaign spokesman, "the South won't save him."

"It's Maginot Line thinking on their part," says William B. Lacy, Dole's campaign manager. But the converse is equally the case. If Bush gets over the early hurdles without mishap, he could head to his southern base with all his opponents grossly overburdened with alibis and desperately short of campaign cash. A cinch, in short.

The operative question for the GOP contest thus becomes whether Bush stumbles in the early tests. And the evidence is that he could. Among the possibilities:Hawaii: Almost unnoticed, Hawaii has scheduled the earliest precinct caucus/straw vote in the nation for Jan. 27. Dole has targeted the state, signing up Rep. Patricia Saiki, the state's only Republican federal elected official, and the GOP leaders of both houses of the legislature. Michigan: Bush is scrambling to avoid embarrassment at the Jan. 29 convention. Volunteers recruited by Robertson, operating in alliance with less numerous backers of Kemp, challenged pro-Bush "regulars" in elections for precinct delegate spots last year and they now control the state committee. That committee meets Sept. 15 to decide a rules dispute on credentials for more than 1,000 additional "regular" delegates, people who ran for state or county office last year. The committee is likely to reject them, setting the stage for a court fight that the Bush camp thinks it can win. With a court victory, Bush backers expect to win a plurality of the national convention delegates to be elected at the state convention. If they fail -- a distinct possibility -- it would be a real black eye because expectations are high in a state whose primary Bush won in 1980. Iowa: Bush has nurtured the organizational and personal ties he forged in his 1980 victory over Reagan and has been rated the favorite for the Feb. 8 caucuses. The latest Des Moines Register Iowa Poll, published Sunday, shows him in a tight race with Dole, although such surveys are not reliable predictors of caucus results. The survey of 301 likely caucus-goers found 32 percent for Dole and 29 percent for Bush, a statistically insignificant difference. Kemp had 10 percent; Robertson, 7; du Pont, 5, and Haig, 4.

Dole, with help from associates of Sen. Charles E. Grassley, has built his organization to the point that Mike Mahaffey, the state GOP chairman, says, "I see both Bush and Dole organizations in every county I visit." Kemp has won some county straw votes this summer and will, like the others, attempt to make a showing in the straw vote at the statewide GOP "cavalcade" in Ames on Saturday. New Hampshire: The first primary occurs Feb. 16 in a state with terrible memories for Bush, the state where Reagan recouped politically in 1980 and humiliated Bush personally at their Nashua debate. If Bush is wounded in the early going, this is the place his rivals think they can damage him beyond repair. If he survives the early tests, New Hampshire may be their last chance to derail him.

Bush has allied himself with New Hampshire Gov. John H. Sununu, former governor Hugh Gregg (his 1980 chairman) and Gregg's son, Rep. Judd Gregg. But the others have all found significant allies. Kemp has the most prominent conservatives, Sen. Gordon J. Humphrey and Rep. Robert C. Smith, in his corner, and his reputation as a tax-cutter serves him well. Dole, moving into the moderate camp that was first lined up for Howard H. Baker Jr., has put himself in the hands of allies of Sen. Warren B. Rudman, and eventually may win Rudman's endorsement. Du Pont has campaigned in the state assiduously and is drawing friendly editorials from the Manchester Union Leader, an important influence, while Haig has spent almost 30 days campaigning in a state where he virtually must finish in the top three to survive. Minnesota: The Feb. 23 precinct caucuses have drawn more attention from Kemp and Dole than from Bush. With Rep. Vin Weber and others allied to the New Right-religious wing of the GOP flying his banner, Kemp has won the straw votes at the last two state conventions. Weber concedes that Dole "has come on very strong" in organizational terms over the summer months, attracting 1986 gubernatorial nominee Cal R. Ludeman, a conservative, and several leaders of the establishment moderate Republican wing as well. Bush has a base among the Twin Cities' suburban Republican moderates, such as Rep. Bill Frenzel, but the state does not appear to have high priority for him. South Dakota: The Iowa results will have an impact here, as in Minnesota, but Dole is seen as the early front-runner in the Feb. 23 primary, even by House Speaker Deborah Anderson, head of the Bush campaign. Dole's edge comes partly from being a Kansas neighbor and farm spokesman but more because he latched on to the organization that nominated and elected Gov. George S. Mickelson last year.

Maine: Bush, with the backing of Gov. John R. (Jock) McKernan Jr. and Rep. Olympia J. Snowe, and with his summer home in Kennebunkport, is a strong favorite in the Feb. 26-28 caucuses that wind up the early voting.

In early March, the spotlight will swing to the South, and the race -- if there still is one -- will likely have lost some contenders and reshuffled the rest. But long before that, Republican voters everywhere will have had an opportunity to watch the six contenders compete in televised debates.

The five others are eager to get on stage with Bush, whose history as a debater has not been a happy one. Bush tried to have the first major GOP debate delayed, then agreed only reluctantly to William F. Buckley Jr.'s "Firing Line" encounter on Oct. 28.

The debates are particularly important to those now seen as long shots for the nomination. Haig has the least money and organization and some of the highest negatives in the field. But his strategists say they think that is largely because voters know him only from crisis situations in the Nixon and Reagan presidencies and rarely have seen him display his sense of humor, business credentials, expertise in foreign policy and a re'sume' that rivals or surpasses that of Bush. Haig dissents from GOP orthodoxy on almost everything from the Strategic Defense Initiative to the balanced-budget amendment and hopes to exploit those differences. But for now, despite relatively high name familiarity and poll standings, Haig tends to be dismissed by his rivals.

Du Pont, who has been more adventurous on issues than anyone else, hopes that something campaign manager Bob Perkins calls "unscripted reality" offers a chance of establishing him as a contender. Bush strategists fear that if du Pont's campaign ever caught fire, he could be as tough for Bush as Gary Hart was for Walter F. Mondale in the 1984 race. But at the moment, he is clearly in the second tier.

Robertson, expected to become an avowed candidate after Sept. 17, is the hardest for the others to figure. His allies in evangelical churches offer him an effective network for recruiting workers, as Michigan showed. His manager, Marc Nuttle, is modest in his claims of what Robertson will do in Iowa or New Hampshire but says he can come on strong in the South. He has the most to gain from the debates. "All we want is to be judged on issues," Nuttle said. Rival camps say it is unlikely Robertson can appeal to many outside the flock who share his religious outlook.

After a somewhat stumbling start, Kemp has made himself a competitor -- if not yet a threat -- to Bush and Dole. His efforts to consolidate his position as the conservative heir apparent have been aided by Laxalt's withdrawal and the emergence of foreign policy issues -- in arms control and Central America -- on which he can rally his chosen right-wing constituency. Kemp strategists contend that this constituency is a potential majority if he gets to the South as the main alternative to Bush.

But Dole blocks his way. The Kansas senator has a difficult double strategy of courting the right wing on foreign policy while simultaneously making himself available as a vehicle for moderates disillusioned with Bush's adaptation to every phase of Reagan's philosophy. He is campaigning hard and allowing others to organize for him, something skeptics doubted he would do. But his mind often seems to be on the Senate, and Lacy says that "my personal opinion is he'll be staying on for awhile" as its Republican leader. It is a choice the campaign obviously does not cheer, even though Elizabeth Hanford Dole, with her travels as transportation secretary, may be the most effective surrogate any of the campaigns can boast.

And then there is Bush. "All he has to do to win," says one longtime associate, "is be as good as the campaign structure that's been put in place for him." In the end, many would agree with Dole chairman Ellsworth's comment: "Bush has to lose this nomination before any of the rest of us can win it."