The State Department brought its SALT-selling road show to Iowa on Friday, running through carefully prepared speeches and charts for an audience of influential Iowans who listened politely if skeptically to an unusual piece of executive-branch salesmanship.

Bankers, industrialist, lawyers and labor leaders-nearly 300 pillars of the Iowa establishment-sat through a morning of lectures and a luncheon speech by Paul C. Warnke, who recently resigned as the United States' principal arms control negotiator. It was the 17th time the State Department had put on this show for a group of heartland "opinion leaders."

The object of the exercise is to duplicate the Carter administration's success of last year when it won support from Mid-america during the Panama Canal treaties debate. But the strategic arms limitation treaty is a trickier matter, as the reaction of participants here suggested.

Collins Bower of Massena, Iowa, an official of the Iowa Farm Bureau Federation, made a representative comment at the end of the program:

"It was good information they gave us, but I don't know if it was complete information."

Or, as a lawyer from Dubuque put it, "we heard one side of the argument very well presented."

More precisely, they heard a mass of detail about SALT H, much of it expressed in a vocabulary that most Iowans-like most Americans generally-find as foreign as Greek, plus analyses of Soviet society, Soviet-American relations and the broad objectives of arms control from a total of five speakers.

Conversations during lunch and after the final speech suggested that this was an overdose for many of those present, particularly those who had never tried before to cope personally with the issues raised by SALT.

Many in the audience seemed o be impressed by one or two things they heard-or that they thought had been ignored. At one luncheon table, for example, the conversation covered these points:

If the United States has a completely adequate nuclear arsenal (a point made by two speakers), why bother with SALT II at all? "Why don't we let our own economic mechanism control how much we spend on these arms?" asked Lyle C. Smith, and executive of the U.S. Postal Service from Waukee.

Why are we so ignorant about the coming generation of Soviet leaders? Can we risk a treaty when we are so ignorant? (Sherrod B. McCall of the State Department's Soviet desk had told the group the United States has very little information about the people who might take power in Moscow five or 10 years from now.)

"Doesn't their history suggest they'll cheat on this?" as Ellwood F. Curtis put it. Curtis is the vice chairman of John Deere & Co., the giant manufacturer of farm equipment.

No one at the table was prepared to argue against SALT II, and several at least had been favorably impressed by the State Department's speakers. But no one wanted to express a strong personal endorsement of the treaty, either.

It was not possible to poll the participants systematically at the Des Moines conference, but Sen. David Durenberger (R-Minn.) did poll those who attended a similar SALT-selling presentation in Minneapolis-St. Paul in late February. Vice President Mondale was the principal speaker there.

Forty percent of those present responded to Durenberger's written questionnaire, and it contained good news for the Carter administration: About a third of the respondents went into the meeting favorably disposed toward SALT II, but afterward 77 percent said they favored ratification.

On other occasions the meeting have gone less well, according to some participants. A State Department official who took part in a Birmingham session, for example, said the pro-SALT speakers had been out-argued there by retired Lt. Gen. Daniel O. Graham, former director of the Defense Intelligence agency, an opponent of SALT II who also was invited to speak.

State Department diplomats aren't comfortable "street fighting" with SALT opponents in a debate, this official observed. "We're information providers," he added. "If the administration really wants to win the debate for public opinion it will have to send out some political types, too."

There was no street fighting in Des Moines. The speeches given by three diplomats and the general counsel to the Arms Control and Disarmament Agency were mostly low key, orderly and to the point. There was no critic of SALT II on the program here-none had asked to speak, according to the president of the chamber of commerce, which organized the event.

Only one man in the audience asked pointedly hostile questions. He identified himself as "Darrell Kearney, private citizen," but the program listed him as a representative of Roger Jepsen, Iowa's new conservative Republican senator who has aligned himself with Senate hardliners.

Even without an opposition spokesman, though, the meeting here included many elements of the SALT debate that is heard in Washington. Particularly characteristic was the constant shifting back and forth between large principles ("nuclear war is a danger that must be avoided") and arcane details ("The Soviets' SS18 missile could have 30 or 40 warheads without SALT II").

As it has in Washington, the verifiability of SALT II - the degree to which the United States can see for itself that the Soviets live up to the treaty's term - emerged as the single greatest concern, at least among those Iowans who stood up to ask questions here.

The government speaker who first addressed that subject was Thomas Graham Jr., general counsel of the arms control agency. In his speech he failed to mention the recent loss of U.S. monitoring stations in Iran, a blow to U.S. intelligence capabilities that is obviously going to be important in the SALT debate. But R.M. Westerfield, a newspaper publisher of West Union, quickly called Graham on that omission, provoking the official to acknowledge that "the bank of uncertainty has widened" because the Irnaian listening posts were lost.

Warnke addressed the verification issue directly in his speech, and seemed to make a better impression.

The ultimate point of this State Department sales program is to win votes in the Senate. Iowa's other senator, John C. Culver, a Democrat, was in the audience here. But in Iowa, at least, the SALT-selling campaign is unlikely to change any vote. Culver is clearly for the treaty, and the conservative Jepsen seems a sure vote against it.

The conference here was paid for by anonymous contributions from ment has spent more than $100,000 sending its officials around the country to speak at similar meetings.