As many as 1 in 5 Americans who want health care plans through the new federal insurance marketplace may be unable to sign up online even if the Obama administration meets a Nov. 30 deadline for fixing the website, according to government and industry officials familiar with the project.

An internal target that administration officials have not made public is the first concrete performance standard since the government began to design the system. It is now guiding the work of hundreds of government employees and contractors racing to try to repair the balky website. The goal is that 80 percent of people going to healthcare.gov should manage to enroll electronically, but that means many others will be unable to get in.

Whether the government meets the benchmark — and whether the public regards it as adequate — will be a central factor in President Barack Obama's efforts to increase support for the controversial health care law and lure customers to the federal insurance marketplace.