President Carter, who got his first big boost on the road to the White House in the cornfields of Iowa, returns here Friday facing an interesting paradox.

He is in deep trouble within his own party. Farmers are mad at him. organized labor has put together a movement to force Sen. Edward M. Kennedy D-Mass.) into the 1980 presidential race. And the president's standing in polls here is miserable.

But Carter is looked at as a tactical genius within the Republican Party.At least two GOP hopefuls are modeling their campaigns here after Carter's 1976 effort. And a host of other candidates are gearing their strategies accordingly.

"No one dares ignore us," says Jerry Mursener, state GOP political director. "Everyone knows there could be a lot of political tombstones in the cornfields of Iowa next spring."

The reason: Iowa is the first step in the long and grueling presidential nominating process. And ever since Carter, then an obscure former governor, used a minor victory here in 1976 to propel himself into national prominence, the state's precinct caucuses have taken on a symbolic importance far greater than the state's size would warrant.

Lesser known candidates, like Republicans Rep. Philip M. Crane of Illinois and George Bush of Texas, know they must do well here and in the New Hampshire primary a few weeks later to keep their hopes alive. They don't necessarily have to win. They just can't lose too badly.

From-runners, like Ronald Reagan, know they have to prove they are as strong as everyone thinks they are.

This hasn't been lost on Carter.

Despite the fact he has no announced opponent, he has already launched his 1980 offensive here, as evidenced by his scheduled appearance Friday before a group of county officials. His son Chip paid a well-publicized visit here last month.

His campaign has a full-time organizer working here. Another is coming soon. Thier job: to keep the president from being embarrassed in Iowa.

"You can take a look at the Iowa poll and see there isn't a love-in for Jimmy Carter here," says one Carter aide.

The poll, released in February by The Des Moines Register, showed that only 17 percent of those surveyed favored Carter, compared with 40 percent for Kennedy and 12 percent for California Gov. Edmund G. (Jerry) Brown Jr.

Equally threatening is the group of top labor leaders who one month ago launched the first major effort to draft Kennedy. The group, which includes key members of the United Auto Workers union who helped Carter in 1976, has been meeting weekly.

It intends to hold regional meetings in 17 cities this month, and set up a headquarters with a paid staff in September.

"If labor and Democratic progressives have left Carter, then he has, in effect, lost two-thirds of his party's support," the group theorized in a draft position paper. "If this erosion can be graphically demonstrated, an alternate candidate must come forth to maintain the Democratic White House."

The White House is responding by massaging the egos of former and would-be supporters. How successful this sort of thing is remains to be seen. One case in point: On Jan. 31, Carter telephoned Viva DeGrado, one of his delegates to the 1976 convention, to ask about her health. DeGrado, who had had an operation, has naturally thrilled. But when she came to Washington last week to attend a union meeting she was wearing a Kennedy-for-president button.

"I am frustrated and confused," she said. "I think all of us are who work in factories. We're all groping for something new and better.

Elaine Smith, whose husband raises hogs in eastern Iowa, and a lot of other conservatives like them, think Republicans have just such a man-

The next one here is May 21, when former secretary of state Henry A. Kissinger is scheduled to speak at a statewide Republican fund-raising dinner. The Des Moines Register has announced that it will take a straw pol of the presidential preferences of all present at the event.

Knowing that a high score in the poll may give its candidate a boost, each camp is nervously eying the date, pondering how to better its standing.

Each of the major GOP candidates has made at least one trip to the state since last summer. Borrowing on Carter's 1976 strategy, Crane and Bush have made repeated forays and have an organizational edge. But Baker and Reagan have both had full-time political operatives in the state during recent weeks.

The state is basking in the attention. The state Republican Party has opened its files and mailing lists to all comers. It has started publishing a newsletter titled "Countdown to Caucus," just for presidential candidates, and it is recruiting candidates to appear at fund-raisers around Iowa to help wipe out the state party's quarter-million-dollar debt.

Bush, a former national Republican Party chairman, has picked up much of the party's moderate establishment, while Reagan and Baker have recently launched less visible organizing efforts.

But Reagan's problem in 1980 is different than those of any of the other Republicans. As the front-runner, and the man who almost beat Ford in 1976 here, Reagan has to prove that he can still win. Much of his campaign network from four years ago is still in place.

"What we have is a bunch of people who have an investment in Ronald Reagan," one Reagan aide said. "What our game has to be is to consolidate what we already have, and to make sure that new people will feel comfortable with us."

Phil Crane. They're betting he'll be the next Jimmy Carter in Iowa.

It's a long-shot bet, most of them admit. But not nearly as much so as it was a few months ago, when Crane was often dismissed as little more than a fringe candidate here.

"It's a word-of-mouth thing," said Smith. "People are starting to come to me asking, 'When can I get some Crane bumper stickers? When can I get some brochures?'"

Smith, a staunch Reagan supporter in 1976, has recently become Crane's Iowa campaign chairman. She thus has a vested interest in such hyperbole.

But most observers agree that Crane has become a credible candidate here, a force to be reckoned with. After months of spade work, Crane's repeated visits to the state have begun to pay off, and he has gotten an organizational lead over better known GOP presidential contenders like former Texas governor John Connally, Senate Minority Leader Howard H. Baker Jr. of Tennessee and Sen. Bob Dole of Kansas, the party's 1976 vice presidential nominee.

The most tangible evidence of movement on Crane's part is a survey of Iowa GOP leaders by the Baron Report, a political newsletter.

Asked who they thought would win the state's presidential caucus next Jan. 22, 47 percent of the respondents said Reagan, 13 percent Crane, 29 percent Connally, 8 percent Baker, 8 percent Iowa Gov. Bob Ray, 8 percent former CIA director Bush and 2 percent former president Gerald Ford. Asked who would come in second or third, 41 percent said Crane, 36 percent Baker, 35 percent Connally and 20 percent Bush.

What all of this means to the average voter is hard to tell. Only about 10 percent of the 460,000 registered Republicans in the state are expected to take part in the caususes in 2,600 precincts. And the political process at this stage of the game moves slowly, almost glacially.

But the Baron survey is one of the few yardsticks to latch onto. CAPTION: Picture, The lure of the Iowa caucuses brought Democratic candidates Sen. Birch Bayh (D-Ind.), Jimmy Carter, former Oklahoma senator Fred Harris and Pennsylvania then-governor Milton J. Shapp to the state in 1976. UPI