"The question is can the Democrats blame all the problems of Iowa on me?" Republican Gov. Terry E. Branstad said woefully the other day as he boarded a plane for a trip to yet another economic development meeting.

Democrats here are betting the mortgage money they can. With Iowa farms and small towns in their biggest crisis since the Great Depression, party leaders think they have a lot to work with.

"We're going to make this election a referendum on economic growth," said Democratic gubernatorial candidate Lowell Junkins. "Four of five young people who graduated from Iowa universities this spring didn't even pause to look at Iowa for their opportunities; 10,000 to 12,000 farmers have been forced off their land; small businesses are being boarded up and 30,000 Iowans have left the state. We've been exporting our most precious commodity -- young people -- like they were corn and beans."

On the eve of the biggest primary day of the year, Junkins, a former state senate majority leader, held a commanding 2-to-1 lead over Lt. Gov. Bob Anderson and state Sen. George Kinley in a heated Democratic gubernatorial primary here.

Iowa is one of nine states holding elections Tuesday. The Hawkeye state, Alabama, California and South Dakota are picking gubernatorial and Senate candidates. In New Mexico, three candidates are locked neck-and-neck for the GOP nomination for governor.

These five states along with Mississippi, Montana and New Jersey, where veteran House Judiciary Chairman Peter W. Rodino Jr. (D) faced a tough race, also have House primaries. A runoff election is being held in North Carolina to pick the Democratic nominee for the House seat being vacated by Rep. James T. Broyhill (R-N.C.) who is running for the Senate.

Iowa and South Dakota, where freshman Republican Sen. James Abdnor faces a tough primary challenge from outspoken Gov. William J. Janklow, will provide two of the year's biggest tests of Reagan administration farm policies.

Branstad, one of only three new Republican governors elected in 1982, has done almost everything possible to try to avert the political fallout from the sagging farm economy. He has made trips to Washington to rail against administration farm policy, visits to New York to woo investors in Iowa industries and journeyed to Hollywood to promote Iowa as a movie state.

Although he has no primary opponent, the 39-year-old governor spent $89,000, a considerable sum in this state, on a slick television advertising campaign. One ad says, "He fought the president of his own party when the federal government ignored our farm problems . . . In less than three years he brought in 100,000 new jobs and signed a moratorium on farm disclosures. Times are tough and Branstad knows it."

But Branstad is in deep political trouble five months before the general election. An Iowa poll, conducted in late May by the Des Moines Register, showed Anderson beating him in a matchup, and Junkins giving him a neck-and-neck race.

There are some signs of improvement in the state economy. Unemployment, for example, is down to 4.7 percent, about 2 percent less than in 1982. Housing starts are at a five-year high.

Most people, however, do not think things are getting better. Seventy-four percent of those surveyed in the Iowa poll described the state's economy as somewhat or very unhealthy.

Branstad's Democratic opponents think his ads may have backfired. They charge his claim on new jobs does not take into account jobs lost, and they note that he had promised to bring in 180,000 new jobs during his 1982 campaign.

"Those ads were the worst thing he could have done because they were too big a distortion," said Anderson, a former high school journalism teacher from Newton. "He had some good will before. But when the ads started running, people laughed him off the streets."

The three major Democratic candidates are in general agreement on the economic health of the state. "Iowa is broke and needs fixing," says a Kinley television commercial. Their disagreement is over what to do about it.

Kinley proposes a one-cent increase in the sales tax and reducing the state debt. Anderson, who is running as the Democrat most electable in the fall, wants to raise $50 million to $75 million for education by limiting the deductibility of federal income tax on state income tax returns.

Junkins has issued the most ambitious and controversial proposal, a $1.5 billion economic development plan financed, in part, with a $500 million bonding program. He would spend the money on research and development, environmental protection and raising teacher salaries.

Junkins, a farmer and longtime political insider, has been endorsed by many labor groups and party kingpins including former governor Harold Hughes. He has also raised far more money than his Democratic opponents.

The great irony of the race is that it has attracted very little public interest. When Anderson, whose Scandinavian name is expected to attract voters, went door-to-door in the small town of Adel on Sunday he encountered this unawareness at the second home he visited: "I didn't know they were having a primary for governor, and I think I'm an informed voter," Jean Evans told him.

Branstad, who lost $33,000 last year on his own farm, says polls indicate that he has the overwhelming support of farmers, although he fares less well among small town residents, a big voting group in Iowa. In an interview, he said he thinks this will be a "very good year" for Iowa Republicans. "Every one of the Democrats wants to either raise taxes or go deeper in debt," Branstad said. Another potential liability for Democrats is a scandal over a stag party staged by lobbyists for a Democratic state legislator in the tiny town of Mingo. A nude dancer and a state representative engaged in an act of oral sex during the party as lobbyists and legislators looked on, according to several present, and a grand jury is investigating the incident.

No gubernatorial candidate had any connection with the party, attended by several dozen Democratic legislators and at least one Republican lawmaker. But Democratic protest candidate Clinton Berryhill, who has proposed a ban on sex outside of marriage, attacked "Mingo-gate" during the primary campaign, saying it "indicates immorality and hedonism and a shift away from traditional Iowa values. "There is not enough religion in the Democratic Party," he said.