DES MOINES, SEPT. 11 -- What do the Great Midwestern Ice Cream Co. and the Iowa Republican Party have in common?

They both are using straw polls this week to make a buck off the '88 presidential race.

The ice cream folks, who operate stores in three Iowa cities, came up with the idea of using the poll as a public relations gimmick.

They've assigned each candidate a flavor with a zany name: "Preppymint" for Vice President Bush, "Born Again Chocolate" for television evangelist Marion G. (Pat) Robertson, "Loquacious Peach" for Sen. Joseph R. Biden Jr. (D-Del.), and "Donna Rice Cream," described as "cheesecake with a slightly tart taste," for former candidate Gary Hart.

A candidate gets a vote every time someone buys his flavor. The gimmick has attracted so much attention that company founder Fred Gratson plans to outfit a bus as a traveling ice cream store and take the show on the road.

"We'll call it the 'Rolling Polling Station,' " he said today.

The Republican Party looks hamhanded by contrast. It is sponsoring a "Presidential Cavalcade of Stars" Saturday in Ames. It could more accurately be described as the "Great GOP Shakedown."

The party is conducting a straw poll at the event, chiefly to build a crowd and help trim its $250,000 debt. It is selling tickets for $25 each.

A ticket buys a chance to sit on a hard gymnasium chair, hear five GOP presidential candidates speak for 15 minutes each and cast one vote in the straw poll. No food or drink comes with the deal.

Most of the presidential campaigns have been quietly seething over the affair since they were told at an organizational meeting last July that the party needed a $5,000 check immediately from each campaign to guarantee choice seats for their supporters.

"They really sucked us all in. We came up with a check," complained one campaign manager. "We had to because of the straw poll."

Among the GOP contenders, only former secretary of state Alexander M. Haig Jr. decided to skip the event, citing a schedule conflict. The other campaigns have been working feverishly for weeks to get as many supporters as possible to the event.

The Bush campaign sent a handwritten note from the vice president to 10,000 Iowa supporters and followed up with hundreds of telephone calls.

"Dear Iowa friend:

"Barbara and I hope your family can join ours at the Presidential Cavalcade in Ames," the Bush letter said. "We need your support at this important GOP gathering."

Sen. Robert J. Dole (R-Kan.) asked thousands of his supporters to buy two $25 tickets each to help him "make a strong showing."

"Since Iowa is the first state in the long presidential sweepstakes, the national press and political pundits will place a tremendous importance on the outcome of the straw poll," the Dole letter said.

To boost his standing in the poll, Rep. Jack Kemp (R-N.Y.) is bringing his top 200 Iowa supporters together for a workshop that will end just in time for them go to the cavalcade. He also rented a bus to take supporters from a "right-to-life" convention to the event, and scheduled a reception for students at Iowa State fraternity house less than a mile from the straw poll.

Bush and Dole, as the front-runners for the 1988 Republican presidential nomination, have the most to worry about from the results of the straw poll. Both are expected to do well.

"This straw poll business is absurd," said George Wittgraf, who heads Bush's Iowa campaign. "Most of us realize straw polls are no accurate gauge of anything, but because they get wide media attention it's necessary for the vice president as the national front-runner to win."

Eight years ago, Bush, who had been getting only about one percent in statewide polls, won a similar straw poll in Ames, giving his campaign a big boost. He went on to win the Iowa precinct caucuses. Dole finished third; Ronald Reagan a weak fourth.

What worries Wittgraf is that Kemp or Robertson, both well behind Bush in public opinion polls, might pull the same kind of showing Saturday.

Kemp surprised Bush and Dole by winning a late June straw poll at a GOP fund-raiser in Polk County (Des Moines). The poll was a rather minor event, but took on major proportions when it was reported on national television and in many Iowa newspapers. "Kemp Tops Iowa Straw Poll," one headline read.

And what about the ice cream poll? Bush got a fast start there when someone purchased a gallon of "Preppymint" worth 40 votes, according to Gary Cassabaum, a franchise owner here. As of early today, Bush had 170 votes; Dole, whose flavor is "Top Banana," had 172, and Kemp had 183.

But Cassabaum said Kemp may have an unfair advantage because his flavor, "Quarterback Crunch," usually sells under the name "pralines and cream" and is the store's most popular flavor.