By the end of this week, states must decide whether they will build a health-insurance exchange or leave the task to the federal government. The question is, with as many as 17 states expected to leave it to the feds, can the Obama administration handle the workload.

“These are systems that typically take two or three years to build,” says Kevin Walsh, managing director of insurance exchange services at Xerox. “The last time I looked at the calendar, that's not what we're working with."

When Walsh meets with state officials deciding whether to build a health exchange, he brings a chart. It outlines how to build the insurance marketplace required under the Affordable Care Act. To call it complex would probably be an understatement:

These marketplaces often get described as a Travelocity or Expedia for health benefits. While that might be the case for the consumer experience, experts say the underlying technology is hugely more complex, a maze of interconnecting computer systems meant to deliver health insurance to 30 million Americans.

"The reality is, states and the federal government are building something new," says Pat Howard, who runs state health issues for consulting firm Deloitte. "There's a rough blueprint in terms of federal regulations, but there's still a number of decisions that need to happen to operationalize this."

A health exchange's first task is ensuring that those who are eligible for benefits know about them -- right now, research suggests three-quarters have no idea.

That suggests a huge outreach challenge -- and one the federal government may not be ideally suited to completing. Evidence suggests that it works better when it caters to local markets. Massachusetts, for example, saw high enrollment after it partnered with the Red Sox to promote its health-insurance exchange.

After people become aware of benefits, the health exchange faces its biggest challenge: Figuring out who is eligible for what. In many states those who earn less than 133 percent of the Federal Poverty Line are eligible for Medicaid -- except if the state has already extended benefits to an even higher level, as 35 states have for children. 

"There may be different family members eligible for different programs," says Sam Gibbs, vice president of sales at eHealthInsurance. "There needs to be a technology system that can support that activity, and look at multiple programs for multiple people."

A state can’t figure out how much an individual earns on its own. For that, it needs to ping a federal data hub that does not yet exist.

The federal government recently contracted with the healthcare IT firm QSSI to build that data hub, and they plan to make it available to both the exchanges that states run and those that the federal government sets up. It will determine whether individuals are eligible for Medicaid, subsidies or no benefit at all.

The challenge here is for states, which may have complex Medicaid rules or old computer systems, to actually plug into the federal hub.

"In many states, the Medicaid system is the best technology that the 1980s could offer," says Bruce Caswell, who runs the health-services segment of Maximus, a firm that works on large government data systems. "As a consequence, they might have brittle interface capabilities."

An old Medicaid system, for example, may only have the capacity to send large batches of data each night. That was fine back in the 1980s, when most applications happened by mail. It's less desirable when you have a law that would like to see real-time application processing.

At the same time, Caswell describes these interfaces as "super critical." They make sure the Affordable Care Act actually works and individuals receive the health benefits to which they are entitled.

After eligibility determinations, exchanges need to present a shopping experience. This might be the easiest part for the federal government, as the same consumer interface could work decently well in different states. Nonprofit groups have also been at work on building a model for the shopping experience, which could potentially be plugged in.

There is one part of the shopping experience, however, that will be more difficult to scale: Customer service. Buying health insurance is a lot more difficult than purchasing a plane ticket on Expedia. That likely means setting up large scale customer-support operations, especially when the first open enrollment period starts in October 2013.

Caswell recalls setting up a call center that handled inquiries in Texas, when it moved 2 million people into different Medicaid programs. He had 90 days to find hundreds of consumer assistance staff -- and a facility where they could all fit.

"We had it find a facility, outfit it, recruit and train staff, take in all the work and then shut it down six or seven months later," he says. "That's the kind of agility that would be difficult without a public-private partnership."

The Obama administration has known for awhile that there's a decent chance it could end up doing a lot of this. Now though, they're finding out how big their workload will actually become.

"The federal government was pretty aware by last year that there was a likelihood many states wouldn't run their own," says Kaveh Safavi, who  leads Accenture’s North America health business. "It's definitely been part of the planning process. Now, the execution and implementation is where we'll be watching next."