Hatch said he "hopes my fears are proven wrong."
The senator argues that Obama put politics above the decisions of his military leaders, who have called for a "modest" reduction in troops.
But Hatch's colleague, Sen. Mike Lee, R-Utah, had the opposite reaction to Obama's announcement, saying what the president is doing is exactly what he promised to do when he increased the troop level to 100,000 in 2009.
"I am encouraged the president has followed through on his pledge to begin the drawdown of forces in Afghanistan this summer," Lee said. "The progress that has been made justifies a reduction in the number of troops engaged in intensive combat operations."
Lee may agree with Obama's decision today, but warned that future reductions should be based on "our capacity to eliminate any new terrorist threats."
That's similar to what the president promised, a slow shift to a more targeted war mission focused on suspected terrorists and Taliban insurgents. Obama plans to reduce the number of service members in Afghanistan by 10,000 at the end of the year and by a total of 33,000 by the end of next summer. He cited gains against al-Qaida, including the killing of Osama bin Laden, as justification for the drawdown.
In the House, Rep. Rob Bishop, R-Utah, said he supports the "eventual drawdown of our troops in Afghanistan but it must be done with the full support and direction of the commanders on the ground and not solely for political purposes."
Rep. Jim Matheson, the lone Democrat in Utah's delegation, said that's exactly what has happened.
"I support a drawdown of troops in Afghanistan. I am glad to see the president following the advice of General Petraeus," Matheson said, referencing the commander of the Afghanistan war.
Chaffetz, who has called for the end of the war, agreed with the drawdown but thinks it should be much deeper and faster.
"I'm glad to see some of the troops coming home. I wish we would bring more of them home sooner," said Chaffetz. "We need to refocus the mission on counterterrorism rather than nation building."
Meanwhile, former Utah Gov. Jon Huntsman Jr., who launched his presidential campaign on Tuesday, argues that Obama should have increased the speed of withdrawal.
"We need a safe but rapid withdrawal which encourages Afghans to assume responsibility, while leaving in place a strong counter intelligence and special forces effort proportionate to the threat," Huntsman, who in April stepped down as U.S. ambassador to China, said Wednesday.