Obama rallies Obamacare troops at 'critical time' for program

Obama warned it will be challenging to overcome the skepticism about the plans given an onslaught of headlines about surging premium prices, but he said the stakes are high.

"I think we're at a critical time where we have to show that this program works for people, if they just see what their options are," he told the volunteers, who work in their communities to encourage and assist enrollment.

Americans who do not receive health insurance through their employer or through Medicare or Medicaid programs shop online for subsidized insurance plans starting Nov. 1 until the end of January.

The average premium for benchmark 2017 plans sold on healthcare.gov rose 25 percent compared with 2016.

Obama said tax credits will help more than seven in 10 shoppers get a plan for less than $75 per month, but said many may not bother looking because they have heard about spiking costs.

"We're going to have to clear the bugs off the windshield so people can see the road ahead, and that's where you guys come in," Obama said.

The law has been fought by Republicans in Congress, who said it creates unwarranted government intervention in personal healthcare and private industry.

Several big insurers, including UnitedHealth Group Inc (UNH.N), Aetna Inc (AET.N) and Humana Inc (HUM.N), are pulling out of the online marketplaces selling the subsidized plans, citing bigger-than-expected financial losses.

Aetna Chief Executive Mark Bertolini said on Thursday that the earliest his company may return to the marketplaces would be 2019.