It could have been a metaphor for the way things have gone lately for many farmers in the Midwestern grain belt. Darrell T. Ringer's 1980 farm pickup, which doubles as his congressional campaign vehicle, blew a head gasket the other day.

For most of the year, Ringer, 31, a wheat farmer and House candidate from Quinter, Kan., has been traveling the state's huge 1st District on what most see as a mission impossible -- trying to paint the blame of Reagan administration farm policies on an incumbent Republican in a GOP stronghold.

"In October 1980, the statewide average price for wheat was $4.05. Today, it is $3.35," Ringer said. "Interest rates did not peak until Ronald Reagan took office, and for three years, we paid 17 percent on our money. I voted for Reagan in 1980 because he said the right things. But the right things have not occurred."

Ringer is echoing a theme common in House races across the Farm Belt. Democrats point to increasing farm failures, unsteady prices, lower exports and continuing high interest rates as products of administration insensitivity. Even with that, two-term Republican Rep. Pat Roberts of Dodge City is regarded as a clear favorite to defeat Ringer.

Despite the problems that nag at farmers, national Democratic campaign officials say a status-quo outcome in November would be regarded as a Democratic victory.

GOP strategists, with more than a dozen races in Midwestern districts targeted for extra spending, think their candidates will gain seats on the strength of Reagan's popularity, the general economic upturn and a residue of farm-country resentment over the 1980 "Carter-Mondale embargo" of grain sales to the Soviet Union.

There is a middle view of unpredictability, however.

"Everything has gone bad in agriculture," said Rep. Richard J. Durbin (D-Ill.). "But there are virtually no coattails anywhere. People will split their ticket in every direction."

Durbin, elected in 1982 with 50.4 percent of the vote in a predominantly Republican farm area and favored to return to Congress, is an example. Reagan carried the district easily in 1980 and is expected to do so again. But in a recent poll, Durbin found that farmers there disapproved of the administration's farm policies by about 2 to 1, although they favored Reagan heavily over Walter F. Mondale.

Durbin's race against Richard G. Austin, a county official from Springfield, is one of four hotly contested House races in heavily agricultural Illinois. The key matchup appears to be in the 17th District, where Rep. Lane A. Evans, a freshman Democrat from Rock Island, is battling a former GOP state senator, Kenneth G. McMillan.

Evans, a strong opponent of Reagan's domestic policies and a member of the House Agriculture Committee, has concentrated on constituent service and has gone home nearly every weekend. But he is under fire from the influential Illinois Farm Bureau and McMillan, who hammers at the theme that Evans is too liberal for the district.

The Evans-McMillan match takes on special significance for agriculture. The district is the home of Agriculture Secretary John R. Block, whose chief business partner earlier this year got a controversial $400,000 low-interest federal farm loan. And the farm recession has had a sharp impact on sales and employment in the huge farm-implements complex around Moline and Rock Island.

Democratic hopes run high in another major Illinois GOP farm area, the 19th District, which includes Champaign-Urbana and features a rematch between Rep. Daniel B. Crane (R) and Terry L. Bruce, a Democratic state senator.

Crane won with 52 percent in 1982, but there's a difference this time. Many now give Bruce an edge because of Crane's censure by the House last year on charges of sexual misconduct with a female congressional page.

In Illinois' rural 22nd District, former representative Kenneth J. Gray (D) is vying with Randy Patchett, a state's attorney, for the seat vacated by Rep. Paul Simon (D), who is running for the Senate. Gray, a flamboyant figure on Capitol Hill for 20 years before he retired in 1974, is a slight favorite.

In many ways, the big House fight in neighboring Iowa's 5th District is a microcosm of the GOP-Democratic differences over farm policy. Rep. Tom Harkin (D), always popular in the traditionally Republican farming district and a harsh Reagan critic, is running for the Senate.

Drought and the unstable agricultural economy have knocked farmers for a loop there, and Democrats are counting on a strong showing by Harkin to help lift Jerome D. Fitzgerald, an experienced state legislator, to victory over Jim Ross Lightfoot, a folksy former farm radio broadcaster supportive of Reagan's farm policies.

Republicans are counting on gains in Missouri, Minnesota and Indiana agricultural areas.

In Minnesota, two freshman Democrats and Reagan critics, Reps. Timothy J. Penny and Gerry E. Sikorski, are in tight fights. Agriculture Committee member Penny, the first Democrat elected this century from the southeast district, is pitted against Keith Spicer, a feed-company executive widely known among farmers. Sikorski is matched against a "pro-life" conservative, lawyer Patrick Trueman.

In Missouri, four-term Rep. Harold L. Volkmer (D), a conservative on the Agriculture Committee but a frequent opponent of Reagan farm policy, is facing Carrie Francke, 30, a former state assistant attorney general and strategist in Sen. John C. Danforth's 1982 campaign.

In east-central Indiana, conservative Republican Ken MacKenzie is pitted against Rep. Philip R. Sharp (D), who came to Congress in 1974 and has warded off strong GOP challenges ever since. Democrats, with a popular prosecutor named Michael P. Barnes, think they will regain the 3rd District seat in South Bend that went to Rep. John Patrick Hiler (R) in a 1980 upset of John Brademas.

Another apparently close race is around Evansville, where Rep. Frank McCloskey (D) faces Richard D. McIntyre, a young conservative who has run ahead of Reagan and Sen. Richard G. Lugar (R) in his successful state legislative races.

In the upper Plains, Reps. Byron L. Dorgan (D-N.D.) and Thomas A. Daschle (D-S.D.), both vehement and frequent critics of administration farm policy, are regarded as probable winners despite the president's popularity there.