The rollout of Obamacare later this year is likely to bring a rate shock for many Americans who will buy health insurance from state marketplaces known as exchanges.

How much will premiums jump? Officials at the U.S. Department of Health and Human Services won’t say. Yes, HHS has received rate filings from insurers. But the agency won’t release rates until September, when the final contracts are signed. That’s only a month before these new exchanges are supposed to open for business nationwide.

HHS officials say they’re still negotiating with insurers and want to drive down prices. They say divulging all this information could confuse consumers or spook insurers.

It could be that HHS is keeping a lid on rates because it wants to avoid a California-like debacle.

Last month, California officials crowed that health insurance premiums would fall in their Obamacare exchange. “This is a home run for consumers in every region of California,” said the exchange’s executive director.

But California officials were off base, according to economists who scrutinized the figures.

Some insurers reportedly controlled costs by cutting out the most expensive hospitals and doctors from their networks and by boosting patients’ out-of-pocket payments. “The premiums for the policies that will be offered ... are much higher than analogous plans being sold today,” Daniel Kessler, a professor of business and law at Stanford University, wrote in a Wall Street Journal op-ed.

Bottom line: The cost of health insurance in California and the rest of the country will spike for many people, especially the young. At the same time, millions of Americans will be pushed into fledgling, sure-to-be-glitchy exchanges to buy that insurance.

With roughly 100 days before the Oct. 1 opening of exchanges nationwide, federal and state officials have blown deadlines and remain tangled in regulatory confusion, according to twin reports last week from the Government Accountability Office.

Many states running their own small-business exchanges, for example, hadn’t finished nearly half the tasks that were supposed to have been done by the end of March, the GAO said. Some states have scaled back offerings to meet the deadline. Others have abandoned the idea of running their own markets and ceded control to the feds.

“Whether (the Centers for Medicare and Medicaid Services’) contingency planning will assure the timely and smooth implementation of the exchanges by October 2013 cannot yet be determined,” the GAO noted in a rousing vote of no confidence.

The states are scrambling to install a complex system that relies on computers to share data with the Internal Revenue Service, state tax offices, Medicaid, Medicare and other agencies in order to verify customer information. A consultant for Utah’s exchange told the Wall Street Journal: “Something will be up and running on Oct. 1. It will be full of issues, bugs and technological challenges.” Ack.

The states also need to train tens of thousands of customer service agents to help customers navigate the exchanges. A massive public outreach campaign looms.

No wonder one top Democrat fretted that the Obamacare rollout would be a “train wreck.”

Amazing fact: A recent Kaiser Family Foundation poll found that about 4 in 10 Americans didn’t know if Obamacare was still the law of the land. About 1 in 10 thought Congress had repealed it. More ominous: One in 4 people age 18 to 30 do not believe that insurance “is worth the money it costs.”

Obamacare counts on healthy younger people buying insurance in droves, lest only sick people sign up and premiums explode for everyone. They may opt to pay a penalty instead if insurance is too pricey or the online sign-up is as balky as a 10-year-old computer.

This is not going to be a smooth ride.

The above editorial appeared in the Chicago Tribune on June 25.