An embarrassing third-place finish in the Iowa Republican straw poll Saturday has sent fresh tremors through Vice President Bush's much-vaunted political organization, which apparently failed to anticipate the turnout for both television evangelist Marion G. (Pat) Robertson and Senate Minority Leader Robert J. Dole (R-Kan.)

However, top Bush aides said they plan no major overhauls of their organization nationally or in Iowa and expressed hope that the formal kickoff of Bush's campaign next month would eliminate the complacency they acknowledge has dogged the early phase of Bush's campaign.

"You've got some people out there who have grown too fat," said a senior Bush adviser, who added that Bush has to be "saying things that get people excited."

Rival campaign strategists questioned whether even as a formally declared candidate Bush will be able to spark the grass-roots enthusiasm that helped him carry the Iowa caucuses in 1980. "The fact is they have indeed kept their {Iowa} organization together for eight years, but it is little more than a social club. It doesn't have a mission . . . ." said David Keene, a senior consultant to Dole. Speaking of Bush's organization, he added, "They're like the old pitcher trying to add a curve to make up for the lost fast-ball."

"Listen, we've got a lot of work to do," Bush said yesterday in a campaign trip to Milwaukee. "Pat Robertson came on like gang-busters there. People turned out from all over and he showed a lot of organizational ability."

The straw poll, while symbolically important, involves only about 3,800 Iowa Republicans -- only a fraction of the 100,000 or more expected to participate in the caucuses next February. But the weekend event was a test of organization in which Bush willingly engaged, and his top strategists had estimated Friday that he would win it by turning out 900 supporters to a $25-a-person party fund-raiser at Iowa State University.

However, they were completely surprised when the Robertson and Dole camps each purchased more than 1,000 tickets the afternoon before the event, and triumphed over Bush.

Bush's top campaign advisers said yesterday that they were dissatisfied with the Iowa organization and that they would take tighter control, with deputy campaign manager Rich Bond -- who spearheaded Bush's unexpected 1980 victory in Iowa -- spending more time there in the months ahead. George Wittgraf, a lawyer who heads Bush's Iowa campaign, said he had miscalculated what it would take for Bush to win because his estimates were based on the 1980 turnout and early ticket sales to the Saturday event.

"A lot of our people think he {Bush} deserves to be the nominee because of his loyal service," Wittgraf said. "A lot of them don't think we have a substantial contest on our hands. But we have to motivate our people to let them know that we do, particularly in the early states."

The Iowa straw poll was not the only setback for Bush over the weekend. The Bush and Dole camps sparred over the results of Sunday's precinct caucuses in Puerto Rico, the first step on what promises to be a contentious trail to the eventual election of 14 national convention delegates.

Dole campaign consultant Donald Devine, who flew down to the island for the caucuses, said yesterday that with reports in from about 60 percent of the precincts, Dole was running ahead of Bush by a "2-to-1" margin in the number of delegates elected to Puerto Rico's Republican convention in November.

A San Juan journalist said the Dole headquarters was filled with "buoyant" supporters Sunday night, while aides to the island's GOP chairman and former governor Louis Ferre were "much more subdued."

But yesterday afternoon, after press queries to Bush campaign aides in Washington, Bush's chairman in Puerto Rico, Ferre, telephoned The Washington Post to report that "my personal survey" of leaders in more than half the precincts indicated Bush had won "80 percent of the delegates."

The counterclaims are hard to weigh, because Sunday's election involved only precinct delegates, who are more clearly identified with local leaders and the factional fight over control of the island's Republican organization than with the national candidates.

The GOP convention on Nov. 15 will decide how the 14 national convention delegates are chosen -- whether by a primary or state (territory) convention vote -- and the controlling faction is expected to pick the method that will help its favored candidate.

Today, in Michigan, the Bush organization faces another hurdle when it asks the state Republican committee to allow about 1,200 GOP officeholders and unsuccessful 1986 candidates -- most of them Bush supporters -- to participate in the GOP county conventions Jan. 14. Bush has been struggling for months against an alliance of Kemp and Robertson backers for the support of the approximately 9,000 delegates already picked to participate.

Staff writers David S. Broder and James R. Dickenson contributed to this report.