In a politically moderate state like Iowa, what's the best campaign strategy for a liberal U.S. senator running for reelection against a strong challenge by a conservative Republican?

Many political managers in 1980 would advise the liberal to back away from his record and create a new image designed to appeal to a supposedly conservative mood.

But Sen. John C. Culver, Democrat of Iowa, long ago decided to run on the issues, trusting the voters of his state to make an intelligent choice between his record and the conservative alternative offered by his opponent, Republican Rep. Charles Grassley. And Sen. Culver's decision appears to have been exactly right.

Early this year, political observers in Iowa were saying that Culver was doomed to defeat. The reasons usually given were that Culver was a prime target of national right-wing groups that began to pour money into Iowa for Grassley's campaign and that the senator was courageously -- but mistakenly -- running on his own liberal record.

In March and May of this year, the respected Iowa Poll published by the Des Moines Register and Tribune showed Grassley leading Culver. By June, Grassley's lead in the poll was 17 points. But in August, Culver moved ahead by a point, and in early October the Iowa Poll showed Culver with 48 percent, Grassley with 43 percent and 9 percent undecided. It now looks as though John Culver will be returned to the Senate with a comfortable margin.

What caused this turnaround? For one thing, Culver has taken some strong stands in the Senate and has not been afraid to defend his record on the issues. He has been a strong supporter of the Strategic Arms Limitation Treaty -- a treaty that is anathema to the right wing. Instead of downplaying his role on Senate ratification of the SALT treaty, Culver has taken the question to the voters, patiently and persuasively explaining his position and winning respect -- and votes -- for his candor.

The senator has won high marks for his voting record from such groups as Americans for Democratic Action, the AFL-CIO, the National Education Association, the National Farmers Union, the League of Conservation Voters and the Consumer Federation of America. In contrast, Rep. Grassley has a very low rating with these organizations.

Iowans thus know where John Culver stands, and he has a strong, active, organized constituency. He has been making steady gains among teachers, blue-collar workers, the young, small-town residents and women. Organized labor is making a powerful effort for his reelection.

One big advantage for Culver is that attacks against him have aroused his campaign workers and supporters. They see their senator as the target of a vicious political assault, financed in large part by reactionary forces outside the state. Culver's partisans know that their candidate stands for something we're all fighting for, and their enthusiasm is the kind of intangible that wins elections.

The Culver reelection campaign is refreshing. Here you see no careful media packaging of a candidate, no ducking the issues, no fear of a well-informed electorate. Instead you find a politics of integrity and openness, with a candidate who gives voters reason to believe in him and work for him.

John Culver, if he were to be defeated, would be losing an honorable campaign based on courageous public service. But the good news out of Iowa is that he almost certainly will win -- and victory will come because the senator has a record of leadership and forthrightness on the issues, and the voters have responded favorably.