With sign-up season launching this weekend, the Obama administration sharply dialed down expectations Monday for the second year of the president's push to provide health insurance for all Americans.

A report released Monday by the Department of Health and Human Services estimated that 9 million to 9.9 million paying customers will enroll for subsidized private coverage in 2015. That's significantly lower than the 13 million the Congressional Budget Office had projected earlier this year.

Until now, the congressional numbers have been used as the yardstick for the program's success. The new administration estimate was commissioned by HHS Secretary Sylvia M. Burwell shortly after she took over in the spring.

Critics are bound to accuse the White House of moving the goal posts. "Obamacare" remains unpopular in much of the country, and Republicans will keep crusading for its repeal when they assume full control of Congress next year.

At least one independent nonpartisan expert said either number could turn out to be valid.

"An estimate of 9 million enrollees is just as plausible and defensible as an estimate of 13 million," said Larry Levitt of the Kaiser Family Foundation. On one hand, said Levitt, the law's mandate that most Americans get covered or risk fines would argue for a bigger number. On the other hand, "there has never been a program as controversial and politically divisive ... which could dampen how quickly enrollment grows," he added.

The health care law has a two-pronged strategy for expanding coverage.

People who don't have access on the job can buy taxpayer-subsidized private insurance through HealthCare.gov and state insurance exchanges. In fact, many are required to do so, to avoid fines. Open enrollment for next year starts Nov. 15.

Monday's new estimates were for this group of people, those covered through the health insurance markets.

The other part of Obama's strategy to cover uninsured Americans expands Medicaid to serve more low-income adults in states that accept the expansion. Overall, the number of uninsured Americans has come down by about 10 million this year.

It could be good news for taxpayers if, as the administration believes, fewer people sign up through the insurance exchanges in 2015. That would mean less spending on the program. But it would not be welcome news for hospitals, which might see bigger-than-expected numbers of uninsured people.

The administration said it disagrees with congressional number crunchers about how quickly Americans will come to accept the law, believing that more time will be needed.

Officials said they started with the current number of people enrolled through HealthCare.gov and state markets, which is 7.1 million.

Of these, they estimated 83 percent would re-enroll for 2015, or 5.9 million. Some of the remaining people might become uninsured, but more likely they would pick up coverage through a job as the economy keeps growing, or through another government program, such as Medicaid.

That would leave a goal of signing up 3 million to 4 million new customers for next year.

Community workers say they think it will prove harder to sign people up this year. Even with generous subsidies, some people still struggle to pay their premiums. And those who sat out last year probably tend to be more skeptical of the program. Nonetheless, fines for remaining uninsured will go up in 2015.

Consumers can get an early peek at 2015 premiums now on HealthCare.gov. Window-shopping went live Sunday night.