Mayor Pete Crivaro gave the Rev. Jesse Jackson a key to the city today.

"If this key will open the Iowa caucuses, I'll twist it," Jackson declared.

With a huge grin breaking across his face, he then turned the big, gold key in the air, saying, "Thank you, Mr. Mayor, for giving me the key to the Iowa caucuses."

Jackson, a well-known civil rights leader, was testing the presidential waters here today to determine if they would be warm to a black candidate for the 1984 Democratic presidential nomination.

Iowa, a state with only 41,700 blacks, has never seen a political trip quite like his. It was part revival meeting, part educational seminar, part a running critique of the evils of the Reagan administration.

"We want farms, not bombs," Jackson said repeatedly.

Jackson didn't meet with a single farmer or a major Democratic power broker, but he came into contact with almost every black leader in the city during the day-long trip, and many appeared receptive to his candidacy.

"He hit everyone from the pimps to the preachers at this event alone," Jesse Taylor, a black businessman, said after a breakfast meeting.

It was obvious that Jackson's trip was something out of the ordinary from the moment he stepped off the airplane.

He was greeted by a crowd of chanting school children and six intimidating "security guards" dressed in black from head to toe and carrying nightsticks.

Jackson checked into the Hotel Fort Des Moines, traditionally the "Republican hotel," where visiting GOP politicians stay.

A teary white waitress flung her arms around him, sobbing that she would never have finished high school if she hadn't been inspired by a speech Jackson gave here several years ago.

An elderly woman in the hotel lobby stared uneasily at Jackson and his bodyguards, members of a Des Moines club called "Triple A Security."

"My God, how many of them are there?" she asked. "We live here, you know."

Ed Campbell, a former Iowa Democratic Party chairman who now heads Walter F. Mondale's presidential campaign in the state, and Chuck Gifford, state political director of the United Auto Workers, sat a few blocks away in the bar of the Savery Hotel, the city's "Democratic hotel."

Checking into the Fort Des Moines was Jackson's second big mistake, in their judgment.

"His first was coming to Iowa" said Gifford, a liberal. "You put him out in the streets of Des Moines and he's in political trouble. He doesn't have an audience to play to. The music is different here. It's not a racial thing; things are just different here than they are in the south side of Chicago.

Jackson, who heads the Chicago-based Operation PUSH--People United to Save Humanity, a civil rights and economic development organization--didn't spend any time on the streets of Des Moines. With the exception of a luncheon hosted by Bishop M.J. Digman of the Catholic Diocese of Des Moines, he spent all of his time in the city's black neighborhoods, speaking to large, enthusiastic audiences.

He'd been invited here to help raise money for Tiny Tots, a large day-care center that's in danger of closing because of federal budget cuts, and he devoted most of his efforts to doing that.

But at six public events Wednesday evening and today, Jackson also delivered strong political messages, urging blacks to rally behind a black presidential candidate.

He repeatedly insisted that he wasn't trying to become that candidate. "At this point, I'm investigating the options, pondering the idea, meeting people and arguing the case that a black must run," Jackson said.

"The proposition to me is far more important than the personality of the candidate," he added.

With a booming voice and colorful rhetoric, Jackson argued that none of the current Democratic for Reston. It's on April 9 at South Lakes High School. Registration (for youth through college age and area coaches) is $20 sent to the Reston Youth Baseball Association, P.0. Box 3440, Reston, Va. 22090. presidential hopefuls has given top priority to issues of concern to blacks, and that since blacks now form the more solid bloc in the Democratic Party "it is time for us to renegotiate our relationship so our agenda gets on the front burner."

"There's no Trojan horse that is now running who is going to put our issues in his belly and once he gets over the White House fence, let us out and say, 'take your share,' " he said.

Jackson said the only way for a black presidential candidate to have credibility would be if he were supported by a broad coalition of black leaders.

Some black leaders already have held meetings on this issue and another session is scheduled Friday in Atlanta. Jackson is not here at their behest, and some would prefer someone else if there is a black candidate.

Jackson's trip to Iowa was the first open attempt to attract attention to such a candidacy. He left little doubt about his interest in the race. He also indicated that he plans to visit New Hampshire.

"I do not want to run," Jackson told a press conference today. "But if the machinery is set up, I may choose to run."