AMES, IOWA, SEPT. 13 -- Television evangelist Marion G. (Pat) Robertson shocked his better-known rivals for the Republican presidential nomination here Saturday night by trouncing them in a straw poll at the first big event of the fall political season.

Robertson's victory was a major embarrassment to Vice President Bush, who finished third in voting at a state-wide fund-raising event. Bush has maintained a supposedly well-oiled organization here for eight years and was favored to win.

It was also a setback for Senate Minority Leader Robert J. Dole (R-Kan.), who finished second, and fourth-place finisher Rep. Jack Kemp (R-N.Y.). Both had hoped a strong straw-poll showing would demonstrate the growing strength of the political organizations they are building for the Iowa precinct caucuses, Feb. 8.

Instead, the "Presidential Cavalcade of Stars" provided a showcase for Robertson's political appeal and his organizational skills.

"He gained a lot of respect tonight," said Dole state chairman Steve Roberts. "He's a major force in the caucuses, a force to be reckoned with. We're going to have to work even harder."

"Robertson up to now has been an unknown factor," said Rep. Tom Tauke (R-Iowa), a Bush state cochairman. "This indicates they {Robertson supporters} are real players in the game."

GOP officials said 5,700 tickets at $25 each were sold for the event, at a basketball coliseum on the campus of Iowa State University.

Not only did Robertson supporters outnumber those of his rivals, they were far more intense and enthusiastic.

They were also easier to see and hear. As they arrived in the parking lot, Robertson supporters were issued white campaign T-shirts with red and blue lettering, noisemakers, bags of confetti and toy styrofoam airplanes to toss. An airplane with a "Robertson for president" banner flew overhead.

Inside the coliseum, Robertson backers looked like a wall of white as they chanted, "Go for it, Pat. Go for it, Pat."

Last September, Robertson announced he would become a presidential candidate only if 3 million people signed petitions asking him to do so. He is expected to announce Tuesday that he has exceeded that goal.

Robertson, who heads a Christian broadcasting empire, has attracted thousands of supporters to similar party contests in Michigan, South Carolina and Florida during the past 14 months.

But he apparently caught all his rivals by complete surprise here.

To vote in the straw poll, each person had to present a $25 ticket and an Iowa driver's license. Robertson received 1,293 or 34 percent of 3,843 ballots cast; Dole 958 or 25 percent; Bush 864 or 22 percent; Kemp 520 or 13.5 percent; former Delaware Gov. Pierre S. (Pete) du Pont III 160 or 4.2 percent; former secretary of state Alexander M. Haig Jr. 12, or less than 1 percent; and other minor candidates 30 votes.

"That's pretty good for someone who is an amateur in this business," Robertson said after the results were announced. "I suggest we have a grass-roots organization at the precinct level like no one else."

"What impressed me was the faces of his people," said state GOP chairman Mikahel Mahaffey. "These are people who frankly don't usually come to these events."

The vote was symbolic, having nothing to do with the selection of delegates to the party convention.

But Robertson and other Bush rivals were quick to declare the results were a major blow to Bush, whose campaign has tried to sell him as the inevitable nominee.

"I'd dare say he's going to be slipping in the polls," Robertson said of Bush. "I think this puts some holes in the invincibility armor," said Dole, who has been running neck-and-neck with Bush in Iowa public opinion polls all year.

The day's events held a clear warning for Kemp. After predicting he would at least finish third, he ended up fourth.

He has based his campaign on appealing to "right-to-life" activists and religious fundamentalists. But Kemp beat Robertson by only a small margin, 37 to 31 percent, at a Iowans-for-Life convention before the Ames event.

The straw poll was important for Bush. He won a similar contest held in the same hall eight years ago, giving his 1980 presidential campaign its first big boost.

Saturday night was also the first time Bush has appeared on the same platform as his rivals. He delivered a specially written speech that aides had predicted would lay out themes for the coming campaign. The speech, however, differed only slightly from other Bush addresses.

Bush followed Robertson to the lectern. The reception Bush received seemed flat compared to the cheers that greeted almost every Robertson remark.

"America is looking for a champion to follow," said George Howard, a prosperous insurance agent who serves as a Robertson county coordinator in Atlantic, Iowa. "He comes off like a champion, someone who speaks for me."

"We feel he can get the county back to what it was founded on -- God's principles," said his wife, Sharon.

The Howards brought 16 people with them from Atlantic, a two-hour drive from Ames.

Although they began recruiting supporters from the ranks of their friends and "born again" Christians, Sharon Howard said, "This really isn't a religious thing."

The Howards and hundreds like them were determined to give Robertson a boost by coming here. "I wanted Robertson to do very well. If he doesn't get a strong showing no one will take him seriously," said Dave Wilke, a grocer from Elkader, Iowa. "It's like any sporting event. The people who get the attention are the top two or three teams."

Robertson has a paid staff of seven in Iowa, a far smaller number than his rivals. It gathered 38,000 names on petitions to persuade Robertson to run.

"They are obviously very well-organized, very well-disciplined and very hard-working," said George Wittgraf, who heads Bush's Iowa effort.

Flying back to Washington Saturday night, Bush political director Rich Bond told reporters that he would return to Iowa within 72 hours to find out if the Robertson victory was a short-lived "prairie fire" or a sign of deeper problems for Bush.