His media expert called him "the American eagle," and for a few short weeks he was the candidate who soared. He was the earnest, fresh face of presidential politics, the Texas Yankee with the resume and energy that would not quit.

His picture, jogging ahead of the pack, was on the cover of Newsweek. His name was on television every night. "Big Mo," he told anyone who would listen, was with him.

But now "the eagle" is in a tailspin, his wings bruised and battered.The fresh face of January is etched with the lines of disappointment and defeat of March.

In a remarkably short, George Herbert Walker Bush has become almost a marginal candidate, struggline for survival in the state where he grew up, the state that sent his father to the U.S. Senate.

When the history of the 1980 presidential campaign is written, Bush's quick rise and fall may provide some of the most telling commentary on the state of politics in 1980. "Geez, the ups and downs of this business, the triumphs and tragedies -- it's a bitch, isn't it?" says his media adviser, Robert Goodman.

Bush was the first hot Republican media candidate of 1980, a role he won with his upset victory over Ronald Reagan in the Iowa precinct caucuses. "We came out of Iowa with so much media hype it would have been hard for anyone to live up to those expectations," campaign manager James Baker complained last Tuesday night as Bush was finishing a weak third in the Illinois primary. "George really was the American eagle."

Bush's failure, another adviser says, "wasn't a failure of precint organization or advertising." Rather, it was a failure in character and strategy on the part of the candidate, an over-reliance on momentum.

Bush called the mementum Iowa gave him "Big Mo." He embraced it. He boasted about it. The pamphlets and advertisements his campaign produced talked of little else except momentum and his impressive resume, which includes stints as a congressman, U.N. ambassador, GOP national chairman and CIA director.

When the momentum disappeared after his defeat in the New Hampshire primary, Bush was left naked.

"When you look behind Bush's campaign, there was nothing there. He was a hollow shell," says Dick Bennett, a pollster for Rep. John B. Anderson (R-Ill).

"People were supporting him because he was winning," he adds. "What I'm getting in my polling now is that people think he is a lightweight. "They don't know where he stands."

"We didn't put an issue base under the momentum like we should have," concedes campaign manager Baker. "There's a false perception out there that George Bush doesn't talk about issues."

When Bush advisers are asked where things started to go wrong, they go back to a meeting Jan. 19, two days before the Iowa caucuses, in Bush's suite at the Ft. Des Moines Hotel.

Up to that point, Bush had followed Jimmy Carter's 1976 strategy. He concentrated on organization and nonstop personal campaigning. As for issues, he had tried to be all things to all people, a conservative for conservatives, a liberal for liberals.

Most advisers present at the Des Moines meeting argued it was time to enter a stage two strategy, in which the candidate would identify himself with issues and state out specific differences from his opponents.

"I saw personally that we had created all the right spirit and environment, but we hadn't really introduced the man," says media adviser Goodman, who was not at the Des Moines meeting but attended other sessions where the subject came up.

"George Bush was that new face people were hungering for," he adds. "We had a great advantage in the lack of perceptions of him, really, which meant we could present a fresh perception that would be considered new and different."

Bush rejected the advice. "It was determined that we should not change something that was working," says Baker.

The first holes were punched in the Bush balloon in New Hampshire. He was the front-runner. Everyone was after him. Campaigning in New England, Anderson started calling him a conservative. Campaigning in the South at the same time, John Connally started calling him a liberal.

The Manchester Union Leader bludgeoned him, attacking his staff, his membership on the Trilateral Commission, his stands on gun control and abortion and his role in accepting payments from a secret 1970 Nixon White House fund.

The final, most devastating blow came at a scheduled Reagan-Bush debate in Nashua, N.H. At the last minute, Reagan invited other GOP candidates to join the debate. More than any other single event, the debate symbolized the unraveling of Bush's campaign.

Bush had come off poorly in other candidate forums. He looked ill at ease, nervous. "The eagle performing alone on his own in [television] ads is terrific," says media adviser Goodman. "That debate format is a terrible format for George . . . It's a let-down. You see seven guys instead of the eagle and six others."

In Nashua, Bush froze under pressure and refused to allow other GOP candidates to share the event. "If George had said, "Look, this has gone far enough. Let's all debate," I think we'd have been 10 points better at the polls," says Goodman.

As it was, Bush compounded his mistake by leaving New Hampshire. For the next two days, he appeared on television from his home in Houston, jogging and lounging beside a swimming pool.

Bush lost the New Hampshire primary to Reagan, 50 percent to 23 percent. In the following 14 days, he lost five of the six next primaries to Reagan, twice finishing third. Only a narrow win in Massachusetts kept him from being shut out.

Bush made some mirror strategic adjustments during these primaries, but it wasn't until the campaign for the Illinois primary began in earnest March 12 that he really went on the offensive.

Ironically, Bush already had accomplished his first major objective of the season by this time: eliminating Sen. Howard H. Baker Jr., John Connally and Sen. Bob Dole from contention.

But suddenly there was a new challenge. Anderson, the maverick Republican from Rockford, Ill., had emerged as a serious contender after strong second-place finishes in the Massachusetts and Vermont primaries.

"We got a bad break from Anderson emerging. Just at the point we had gotten to be the alternative to Reagan, along came Anderson," campaign manager Baker says. "Anderson got his media hype just perfect for him -- right before the primary in his home state."

Anderson's outspoken liberalism appealed to independents and Democrats, the same voters Bush hoped to woo. In contrast, the "new Bush" looked contrived and insincere.

Bush, aides announced, would give more major policy speeches. There would be more prepared issues papers. The candidate would henceforth answer questions only about issues. Aides would talk about strategy and tactics.

"Me, I'm the issue candidate," Bush. the candidate who had spent months talking about tactics rather than issues, told a Chicago news conference last Sunday.

The session demonstrated the pitfalls of the approach. The purpose of the news conference was for Bush to issue a critique of Carter's new economic plan. But when he was pressed on specifics, Bush stumbled and stammered. Aides, embarrassed at their candidate's performance, stopped the questioning short and ended the news conference. Bush didn't looked fuzzy; he looked silly and ill-prepared.

Bush's return to his home state this week was laced with symbolism and desperate hopes. "Welcome home" banners greeted him at every stop. "This is the state where I grew up, was educated in, and where my father served with honesty and distinction," the candidate told audiences.

His campaign was still financially sound, with $2.6 million due in federal matching funds. Bush insisted he was in the race to stay, or as he told one audience in Illinois, "The opera ain't over 'til the fat lady sings."

But there was a sense of gloom about his campaign. Reporters found themselves suddenly being reassigned to Reagan and Anderson.

The candidate put on a brave front, attacking Anderson as "the Teddy Kennedy of the Republican Party" and Reagan as a irresponsible warmonger.

"You don't know how good it was to leave Illinois," he said in Glastonbury the other night. "I got clobbered there. Came back here, and made the mistake of turning on the television. You know those mournful-looking guys, they were on saying, 'Well, this spells the end of George Bush,' Hell with 'em. We're going to win this nomination."