Ronald Reagan rebounded today from his narrow loss in the Iowa caucuses to crush the New Hampshire challenge of George Bush by an unforeseen wide margin.

Surprising even his own supporters, Reagan beat Bush 2 1/2 to 1 and won an absolute majority of the vote against six Republican presidential contenders.

Final results showed Reagan with 72,734, or 50 percent; Bush with 33,304, or 23 percent; Howard H. Baker, Jr. with 18,760, or 13 percent; John B. Anderson with 14,622, or 10 percent; Philip M. Crane with 2,633, or 2 percent, and John B. Connolly with 2,215, or 2 percent. Bob Dole had 608, or less than 1 percent.

Reagan won 13 of the 22 delegates at stake in this first state primary, and Bush won five. Baker and Anderson each won two delegates.

"This is the first and it sure is the best," a triumphant Reagan told beer-drinking blue-collar supporters in a Holiday Inn ballroom in Manchester.

Reagan won at least 14 and possibly as many as 16 of the state's 22 delegates. Bush had four delegates and Baker two, Anderson will win two if his final total stays above 10 percent.

Bush conceded less than two hours after the polls closed and congratulated Reagan. Then he told a crowd of cheering supporters at his Concord headquarters that "disappointed as I am, I'm absolutely convinced that we're going to win this nomination."

But Gerald Carmen, architect of Reagan's vigorous on-the-ground campaign here, saw the defeat as more than a temporary setback for Bush.

"I think George Bush is mortally wounded and not just in New Hampshire," Carmen said. "We always knew that if we could puncture George Bush's balloon, there would be nothing there but hot air."

The combination of an intense, bitterly fought primary campaign and more of the clear, mild weather that has prevailed in New England this winter brought a heavy turnout of 145,000 voters into the Republican primary.

They came out for what was expected to be a tight contest between Reagan and Bush, but Reagan jumped into the lead the moment the polls closed and ran away from the field.

He won everywhere. Reagan won three-fourths of the vote in heavily blue-collar, industrial Manchester. He beat Bush 60 percent to 14 percent among French-Canadians, an important ethnic group here. Reagan won 9 to 1 in the small cities, 2 to 1 in the rural areas, 3 to 1 in the towns. He had a 2 to 1 edge over Bush amaong Protestant voters and better than a 3 to 1 edge among Catholic voters.

Reagan had been expected to win heavily among blue-collar workers, where he led Bush 51 percent to 20 percent. But he also defeated Bush 39-15 among white-collar voters.

What happened to produce this margin of victory? As Bush pollster Robert Teeter analyzed it, Reagan was the second choice of many voters who said they were for Bush. Reagan's vigorous campaigning pulled him slightly ahead of Bush in the final days of the campaign.

Then came last Saturday night's dramatic scene in Nashua when Bush was blamed by four other candidates for excluding them from a Bush-Reagan debate. When voters defected from Bush, Teeter said, they went directly to Reagan rather than to any of the other candidates.

Another factor in Bush's defeat may have been his virtual abandonment of personal campaigning in New Hampshire. Ironically, this was the very failing which Bush had capitalized on at Reagan's expense in the Iowa caucuses.

Because Bush's New Hampshire manager, Hugh Gregg, wanted Bush out of the state to allow his organization to perform and because Bush's national managers wanted him to rest before each of two debates last week, the former United Nations Ambassador made no appearances in New Hampshire for the last seven days of the campaign, other than the debates.

Gregg was Reagan's manager here in 1976 when Reagan left the state two days before the primary and was narrowly defeated by Gerald Ford.

"I'm not going to make that mistake this time," Reagan confided to one aid several days before the election -- and he did not.

Today's election was doubly helpful to Reagan because it severely damaged one challenger without raising up another. Baker had hoped to benefit if Bush went down, but the Tennessee senator's vote percentage was less than it was in Iowa.

"Baker had everything happen to him that he wanted -- and nothing happened," said Teeter.

Baker's campaign manager, former Gov. Walter R. Peterson, made a similar point. He said that Reagan was viewed as the alternative for voters who wanted to retaliate against Bush.

"What really was the issue was fair play," said Peterson. "It was an obvious backlash vote."

Baker conceded, but gave no hint that he would drop out of the race.Indeed, he said that "We're now in our second set of front-runners and there will be another one still . . . don't assume for one moment that this race is over."

But Baker now faces an even more uphill battle for fundraising and attention unless he can rebound in southern primaries, where Reagan is considered even stronger than he is in New Hampshire.

Anderson waged a skillfull campaign here, but failed in his goal of finishing in third place ahead of Baker. But he was holding on to enough votes to win two delegates.

"It's a virtual dead heat," Anderson said of his race with Baker. The Illinois congressman told reporters he thought he could still win the presidency and vowed to stay in the race.

Anderson will continue his campaign in Massachusetts, where his goal is to finish second behind Bush, who has been leading there in the polls. gReagan will campaign Wednesday in Vermont, which like massachusetts will hold its primary next Tuesday. "When we go to Vermont tomorrow, we won't need an airplane," Reagan said. "We'll fly there on what happened tonight alone."

The New Hampshire campaign probably marked the ned of the trail for Dole, who was polling about one-third of one percent of the vote, just ahead of the write-in for former President Ford.

Dole said he probably would enter no more primaries. "Obviously there's not much of a campaign out there," he said.

It also came close to extinguishing the slim chances of Crane and it left Connally with the difficult task of building momentum against Reagan in his southern strongholds.

If past performance is a guide, the New Hampshire primary is likely to have a profound effect on Florida, whose Republican electorate has northern roots. In 1976, the polls showed a sudden swing of 14 percentage points in Ford's favor after he defeated Reagan in New Hampshire.

Reagan has been running even or slightly ahead of Bush in Florida polls taken before today's significant victory.