When the campaign for Congress started last fall in Illinois' 22nd district, all seven candidates had a similar problem: how to find money.

By this week, though, the leading candidates had discovered a basic truth of American politics: the money found them.

From northern New Jersey and southern California, from doctors in Chicago and auto executives in Detroit, from Texas, Tennessee, Toledo, and Topeka - and, of course, from Washington, D.C. - thousands of dollars in campaign contributions have poured in to influence the farmers and factory hands here as they choose their new congressman.

The 22nd's sharply positive balance of political payments reflects the importance of "political action committees," the proliferating organizations that gather contributions from large numbers of like-minded people and distribute the money in lump sums to favored candidates.

It shows as well that that the label "Reaganite," pejorative as it may be in liberal circles, is a powerful money magnet on the campaign trail.

The money started coming into this relatively obscure stretch of eastern Illinois farmland last fall, when the 22nd's popular incumbent congressman announced he would not run for reelection in 1978. That news drew four Democrats and three Republicans into a battle for the seat.

The candidates soon discovered that the first $5,000 or so they could raise would be consumed on the basics of a campaign - a telephone and someone to answer it, and a supply of the buttons, bumper stickers, matchbooks, and emery boards that are de rigeur for a political candidate in this part of the country.

Transportation, to, is a major cost factor in the 22nd, where a candidate can drive the distance from Washington to Wilmington and still be in the district. Roscoe Cunningham, for example, the Republican state legislator from Lawrenceville, ran up $1,500 in automobile expenses in the first two months of 1978.

To buy anything else - mailings or media - a candidate here needs big money.

Only one of the 22nd's candidates, Gene Stunkel, a Republican from Danville, the district's biggest city, has found any sizable money close at hand. And he has found it very close indeed - in his own pocket.

Stunkel, a newcomer to campaigning who is convinced he can find the same success in politics that he achieved in a series of businesses over the past 10 years, has given his own campaign more than $70,000. As of last week, he had raised an additional $2,000 from local friends and business associates.

The champion solicitor of outside money has been Dan Crane, the Danville dentist who is a leader of the district GOP's Reaganite bloc.

Crane has a built-in banker in the person of his brother Philip, an attractive, articulate congressman from the Chicago suburbs who is a hero of the first magnitude in conservative circles around the nation. On his brother's behalf, Phil Crane last month sent out 70,000 letters nationwide to veterans of Ronald Reagan's 1976 presidential campaign. That soliciation brought thousands of dollars back to Dan Crane's campaign.

Among those who responded was Ellen Garwood, a cheerful grandmother from Austin, Tex., who knew Phil Crane from the Reagan drive.

Garwood sent Dan Crane a check for $250 the minute she received Phil Crane's letter. She had never heard of the candidate before, and she wasn't exactly sure where the 22nd District was, but all that was secondary. "If this Dan is anywhere half as smart as Phil is," she said recently, "I figured we needed him in Congress."

The Cranes also approached larger sources of political money, and that exhausting effort has borne fruit. By last week the Crane campaign boasted contributions from "political action committees" at corporations in New Jersey and Michigan, from the American Medical Association, and from a number of political groups aligned with the so-called "New Right," bringing Dan Crane's total campaign fund to $58,000.

Cunningham, the Republican legislator from the district's sparsely populated southern sector, has relied more on stirring oratory than on sterling for his primary campaign. By last week Cunningham had raised just $5,900 for his battle against Crane and Stunkel. Of that total, $2,500 came from the Chicago-based Illinois Medical Association.

The state medical association hedged its bet on Cunningham, somewhat, however, by sending a separate $1,000 contribution to Terry Bruce, an aggressive state senator from Olney who is working hard to win the Democratic primary.

With some help from his brother, Ken, who is a lobbyist for Illinois' main teachers' union, Bruce has also received $4,000 from the National Education Association, the Washington headquarters for teachers' groups around the country.

Bruce's total receipts of $13,500 would make him a relative pauper in the 22nd's Republican primary, but in the more austere Democratic race, he is the big spender.

Bruce's chief competitor for the Democratic nomination. Don Watson, has reported total contribution of $9,000. But then Watson, a quiet easygoing sort who lives just down the way from Terry Bruce in Olney, has a campaign asset that money can't buy. He is the brother-in-law of the retiring incumbent congressman George Shipley and Shipley has put his considerable popularity to work on Watson's behalf.

Dave Hill the young Democrat from Mattoon who quit a sweet government job in Washington to come home for the congressional race, has raised $6500 mostly in small gifts from his high school chums. The fourth Democrat. Tim Thut (pronounced "Toot"), whose espousal of liberal causes has kept his campaign in a permanent nose dive, has raised $310.80, all from one source - Tim Thut.

Cunningham, Watson, Hill, and Thut, the under-funded candidates have tried to win voter sympathy by emphasizing their "poor boy" status vis-a-vis their adversaries. But they all say they would gladly give up the sympathy in return for more money to campaign with.

There is, however, one catch in-money: the more a candidate can get, and spend, the more complicated are his reports to the Federal Election Commission.

Last week the candidates had to send in their campaign finance reports for the first 10 weeks of this year, and they all reported it to be an exhausting, and frustating, experience.

One problem is that the directions on the FEC forms seem to have been written by the same bureaucrat who drafts income tax forms.

"Schedule B supports the amounts reported on Lines 20a, 21a, and 22a, b, c on page 2 FEC form 3," one instruction reads. ". . . The checkoff boxes SHOULD NOT be used when itemizing operating expenditures. The "total this period" amount for each itemized line is to be carried forward to the corresponding line of the Detailed Summary of FEC form 3 (page 2)."

"They send you gobs and gobs of forms," says Jerry Lockhart, an author of chunky frame and cherry spirt who has helped Stunkel with his complex campaign reports. "If the candidate sneezes three times one day that's a different form from two sneezes. And if you get it wrong, they send it back."

Terry Bruce, who is considered the most savvy political strategist in the race, also complains that the spending reports might give away his secrets. But he found a way around that problem.

"Last week, we had to report through March 6," Bruce explained with a chuckle. "So when I bought my radio time, I told the stations I'd write them the check March 7. That way I don't have to report what I'm buying until after the election."

Eventually, however, all seven filed their spending reports, and turned their attention again to the main task at hand: winning this Tuesday's primary. With one more weekend of campaigning left to go, most observers agreed that the races in both parties were too close to call.