In just nine months, Californians will begin shopping for insurance in the state's health exchange.

As many as 430,000 people are expected to enroll by Jan. 1, when the main provisions of the federal health care reform law take effect. By the end of 2016, membership is projected to reach 4.4 million.

Supporters envision an online marketplace, something similar to Amazon and other etailers, where customers can compare policies and prices using a computer or smartphone.

Getting that up and running on time is an enormous challenge. So is explaining the program to millions of people and employers who must decide whether to use the exchange — called California Covered.

Obamacare, as the Affordable Care Act is universally known, is more popular here than in many states. As such, officials are further along on implementation. The state exchange was one of six to receive conditional federal approval last week. But given the state's history of bungling computer projects, this one needs plenty of scrutiny.

"None of this is easy," Peter Lee, the official in charge, told the Sacramento Bee, "and we're confident about all of it."

We hope Lee's confidence isn't misplaced. The stakes are enormous.

Seven million Californians — about one in five — lacked coverage in 2011, according to the California Healthcare Foundation. Some of them go without care, others rely on emergency rooms. When they can't pay, the costs get passed on as fee hikes and higher premiums for those who have coverage.

Obamacare aims to reduce the impacts of unpaid care by requiring almost everyone to have insurance. To make it possible, there are premium subsidies as well as an expansion of Medicaid for the poor, and the exchanges are intended to harness the buying power enjoyed by large employers.

California created a similar program 20 years ago — a state-run purchasing pool intended to cut costs for individuals and small employers. After a promising start, the program failed. But the concept still is a good one, and Obamacare's insurance mandate may be what's needed to make it work.

It wasn't until Thursday that Gov. Jerry Brown committed California to the other major aspect of Obamacare — expansion of Medi-Cal, the state's version of Medicaid.

The federal law allows states to offer Medicaid to people earning up to 138 percent of the poverty line. Washington will cover the full cost for the first three years and 90 percent afterward.

About half of California's uninsured are expected to qualify, giving them greater access to health care and, equally important, ensuring payment to hospitals and other providers. That, in turn, will save money for employers and other policyholders who are now stuck with subsidizing the cost of uncompensated care.

The legal challenges to health care reform have failed, and voters re-elected President Barack Obama. In short, the health program that bears his name will take effect in less than a year. The challenges ahead include getting health exchanges up and running, enrolling people in Medi-Cal and educating the public in how to access coverage under Obamacare.

The clock is ticking.