ALEXANDRIA — Gov. Mark Dayton apologized to county officials Wednesday for the troubled rollout of Minnesota’s online health insurance exchange, calling the initial glitches with MNsure the biggest disappointment of his first term.

But the Democratic governor also staunchly defended the federal Affordable Care Act before a crowd of about 200 county commissioners from across the state.

Dayton, who is running for re-election, appeared at a general session of the Association of Minnesota Counties held in Alexandria. He thanked county leaders for their help with MNsure.

“I want to thank you for the tremendous assistance you and your county staffs provided to MNsure, and I want to apologize for the excessive burdens it’s placed on you, your budgets and your people,” Dayton said. Calling MNsure’s rocky start his biggest disappointment so far, Dayton said, “It’s got better, and it will continue to get better, but it still has a ways to go.”

Despite perceptions that problems with the Affordable Care Act could cost Democrats in November, Dayton trumpeted the program.

“Over 300,000 Minnesotans have now obtained health care coverage through MNsure,” Dayton said.

Noting the coverage guarantee even for people with pre-existing medical conditions, he said: “One gentleman told me at the State Fair last week, quote, ‘MNsure saved my life and my wife’s life.’”

Dayton’s Republican opponent, Hennepin County Commissioner Jeff Johnson, also spoke to the group but did not bring up MNsure.

A spokesman said Johnson would prefer to obtain a federal waiver from the Obama administration that would let Minnesota run its own health care system, but short of that, he would seek major changes to the way MNsure operates.

Dayton and Johnson are not scheduled to debate directly until Oct. 1 in Rochester.