SALT LAKE CITY, Utah (Reuters) - Veteran U.S. Senator Orrin Hatch faced what may prove to be the toughest re-election bid of his 36-year tenure, as he battled a challenge on Thursday by two younger Tea Party candidates in Utah's Republican caucus amid high turnout.
Heavily Republican Utah last elected a Democrat to the U.S. Senate more than four decades ago, so the victor in the state's Republican party contest is usually considered the presumptive winner of the general election in November.
For a senior stalwart of the Republican mainstream like Hatch, the ranking Republican on the tax-writing Senate Finance Committee, an incumbent seat in the U.S. Senate has long been seen as his to lose. He was first elected in 1976, turns 78 next week, and says this next term will be his last.
"We're starting to get numbers in and what we're seeing in the reports, and it's more than just anecdotal now, it was a very, very good night for Senator Hatch," his campaign spokesman Dave Hansen said, although no numbers were available.
Hatch was fighting to avoid the fate of his former Senate colleague, Utah's Bob Bennett, whose 2010 run for a fourth term foundered over conservative outrage at the healthcare overhaul pushed by President Barack Obama, leading to a revolt against the Republican establishment by state Tea Party activists.
Former state Senator Dan Liljenquist, 37, and state Representative Chris Herrod, 46, are among the most prominent of nine Republicans hoping to grab Hatch's traditional spot on the ballot, saying now is the time for change.
"It's time for a new generation to step up and lead," Liljenquist said in a recent interview. "Washington will not be changed from the inside."
Herrod described the caucuses as a "good night," adding it was hard to compete against Hatch's resources: "I think this is still a race the nation wants to watch."
Utah Republican Party Chairman Thomas Wright said preliminary estimates put turnout at between 125,000 to 200,000, more than double the number who took part in 2010.
The turnout was causing caucuses to run late and making it difficult for the party and candidates to get news of which delegates were being elected and who they supported.
Both of Hatch's challengers have gained a strong Tea Party following with campaigns focused on conservative themes such as smaller government and less tax. They have suggested Hatch's principles have been compromised by his lengthy tenure as part of the inside-the-Beltway establishment.
MAY NOT SEE CLEAR WINNER YET
Republican voters taking part in the hundreds of caucus meetings throughout Utah on Thursday in homes, churches, schools and other locations were selecting 4,000 delegates to represent them at a party convention on April 21.
The results will give a first significant sign of Hatch's re-election prospects, although a clear winner may not emerge until the convention, or later if a run-off vote is needed.
A candidate who emerges from the convention with 60 percent or more of the party's delegate vote will clinch the nomination.
If no contender takes 60 percent, the two highest vote getters compete in a primary election on June 26, the same day as Utah's presidential primary.
In 2010, Bennett came in third among delegates, and failed to make it out of the convention. Mike Lee won the primary runoff against the second-place Republican, and ultimately succeeded Bennett in the Senate.
Washington-based political action group FreedomWorks, closely aligned with the Tea Party movement, has spent nearly $600,000 to unseat Hatch this year, according to campaign expenditure filings.
But some longtime Republicans in Utah said the mood in the state was not the same as in 2010, when Bennett was pushed out, and that Hatch had positioned himself well going into the night.
"They underestimate how many people he has worked with over the years," said Enid Green Mickelson, a former congresswoman from Utah. "He has always worked hard for his re-election. He's always run like he's opposed."
To boost turnout, party officials stepped up precinct training and paid for lawn signs and television and radio ads reminding voters to attend.
"A real strong Tea Party member and good friend of mine, a little to the right of me, was bringing 50 people along who were supporting him to his precinct," said Swen Howard a legislative district vice-chair for the Republican Party in Davis County, just north of Salt Lake City.
The Mormon Church, which asked congregations to refrain from holding church meetings the same night as the party caucuses to avoid scheduling conflicts.
(Editing By Cynthia Johnston and Tim Gaynor)