Rep. Jason Chaffetz announced Monday that he will run for re-election rather than take on Sen. Orrin Hatch at next year’s Utah GOP convention, a surprising decision that follows months of preparation to challenge the six-term incumbent.

Chaffetz would have been a strong contender to upend Hatch at the Republican convention of 3,500 locally elected delegates. Former Sen. Bob Bennett was ousted at the convention last year by delegates who argued he wasn’t conservative enough, and his loss to now-Sen. Mike Lee gave Hatch an early warning about what was to come in 2012.

Chaffetz has been outspoken in his criticism of Hatch’s voting record. He told Roll Call in June that he was “likely” to run but would wait until the end of the summer to announce his decision.

The Hatch campaign, led by former state party Chairman Dave Hansen, started its counterattack early. Chaffetz would have started the race well behind both organizationally and financially, even with likely assistance from conservative advocacy groups such as the Club for Growth and FreedomWorks, both of which disapprove of Hatch’s voting record. By the end of June, Hatch reported more than $3.4 million in the bank, compared with Chaffetz’s $227,000.

The Hatch campaign has also been working to build up support among party activists seeking to become delegates, who will be chosen at 1,850 local caucus elections March 15. One to three delegates will be elected from each precinct and will be charged with voting at the April 21 state party convention. A candidate can secure the GOP nomination outright by winning 60 percent of the delegate votes; otherwise, the top two finishers face off in a primary. The GOP nominee is usually favored to win the general election in the strongly Republican state.

Kirk Jowers, director of the Hinckley Institute of Politics at the University of Utah and with whom Chaffetz spoke during his deliberations over the past several months, called Chaffetz “the 800-pound gorilla in Utah Republican politics.” Despite Chaffetz’s strong approval among the state party’s delegates, Jowers said Chaffetz’s decision boiled down to where he would be most effective.

“Senate opportunities don’t come up too often, and the polls and everything else looked very good for Chaffetz to make a run, particularly with Utah’s unique election system,” Jowers said. “On the other hand, Chaffetz has been kind of uniquely successful in the House.”

Chaffetz will run for a third term and is likely to be easily re-elected. Utah has not yet approved a redistricting plan, but Republicans control the process.

Hansen, Hatch’s campaign manager, wished Chaffetz “the best in his congressional campaign and in his continued service as one of Utah’s representatives” in a statement Monday.

“Senator Hatch looks forward to continuing to work together as a delegation to find solutions to the critical issues facing Utah and our nation,” Hansen added.