Washington ? As skeptical Americans delve into the health care blueprint approved by Congress on Sunday, they will confront a bargain not unlike those faced by earlier generations of Americans — with Social Security and Medicare.

Much as Franklin D. Roosevelt did for old age assistance and Lyndon B. Johnson for health care for the elderly, President Barack Obama will ask people to accept new costs and government requirements now in exchange for benefits and protections that most will not immediately see, and some may never need at all.

Under the health care plan Obama will sign into law today, millions of retirees will no longer have to worry about gaps in Medicare’s prescription drug coverage. Americans who lose their jobs will be able to get health insurance. And small business owners will get help providing benefits to their workers.

But on any given day, many Americans may not see those new benefits, especially if they are healthy and work for a company that provides them with health benefits.

What wealthy taxpayers will almost certainly see is a tax increase. Others, especially the young and healthy, will be pressured to buy insurance they may not want. And almost everyone will have to file another form with the Internal Revenue Service certifying that they have coverage.

Those trade-offs are critical to make a health care safety network, according to most health policy experts.

There is widespread agreement, for instance, that it is necessary to bring everyone into the insurance pool to restrain costs and make it possible to require insurers to cover everyone.

But the trade-offs make the bargain at the heart of the Democratic health care legislation vastly more complex than the one Roosevelt made in 1935 or that Johnson struck with the creation of Medicare in 1965.

That complexity also makes this new health care bargain potentially much more fragile.

“Politically, Medicare and Social Security are stronger because they include everyone, and therefore everyone has a stake,” said Paul Starr, a Princeton University political scientist and health policy expert. “That does not apply here.”

Further complicating Democratic efforts to promote their health care overhaul is the design of the legislation itself.

Eager to avoid worrying Americans satisfied with the coverage they get at work, Democrats explicitly designed their bill to do as little as possible to the existing employer-based health insurance system.

“That was a necessary accommodation,” said Starr, who said the legislation should therefore not be compared to more traditional safety net programs like Medicare, Medicaid and Social Security.

The difference means Obama and congressional Democrats often are promoting an array of different benefits to different groups of people depending on how old they are, where they work and how much money they make.

Starting this year, for example, insurers will no longer be able to deny coverage to children with pre-existing medical conditions. Adults will have to wait for that protection until 2014.

Single Americans who make less than $14,404 will for the first time be able to sign up for the government Medicaid program.

Americans making more than that who do not get insurance from their employer will be able to sign up for a commercial plan. And millions of those will likely qualify for subsidies to help them pay their premiums.

By September, the health care legislation will bar insurance companies from imposing lifetime limits on what they will pay for patients’ care.