BUENOS AIRES, Aug 14 (Reuters) - Farmers in Argentina, a major global grains exporter, are keen for economic policy changes to boost trade, but said they were concerned over the lack of experience of Javier Milei, the right-wing presidential candidate who took a surprise first place in Sunday's primary.

The outsider libertarian known for incendiary rhetoric received more votes than any other candidate, effectively turning October's general election into a three-horse race.

Some agricultural and rural leaders expressed hope that the result would mean more market-friendly economic policies after a government led for almost four years by the center-left Peronists, long seen as the nemesis of the country's powerful farm sector. But others in the traditionally conservative sector worried about Milei's fiery rhetoric and relative inexperience in politics.

"We don't know him. Of course, (business-friendly) ideas are welcome, but not right-wing populism," said Horacio Daciencio, a rancher from Buenos Aires province. He hinted he might ultimately support Sunday's second-place finisher, Patricia Bullrich, a former security minister who will represent the conservative opposition coalition.

While opinion polls leading up to the primary vote indicated Milei could do well, none predicted that the first-term federal lawmaker from the capital would outperform the center-right opposition or the embattled Peronists.

With nearly all ballots counted, Milei secured 30% of the vote, ahead of the center-right coalition's 28.3% tally and the 27.3% won by the Peronist alliance.

"Citizens delivered a forceful message to all the politicians," said Carlos Achetoni, president of the FAA agrarian federation, one of the country's most important farm lobbies. Achetoni stressed, though, that Milei's track record sparked doubt.

"The countryside needs clear, predictable and stable rules that provide us with opportunities," said Nicolas Pino, president of the SRA rural association, another influential farm group, in a statement.

Farm leaders have traditionally supported market-friendly candidates.

"If I had to ask the new president for something, I'd say two things: unify the exchange rate and eliminate withholdings (export taxes)," added Pino.

Both policies are among Milei's promises if elected president later this year. (Reporting by Maximilian Heath Edited by Nicolas Misculin and Rosalba O'Brien)