WASHINGTON — The Supreme Court will engage this week in a historic three-day showdown over health care, leading to decisions that could ensnare everyone from private citizens to the president of the United States.

During oral arguments longer than any seen since the mid-1960s, the court's nine justices must calculate whether the Obama administration's signature health-care law goes too far and violates the Constitution. The answer — or answers — will:

• Determine who's covered by health insurance.

• Control what laws Congress can pass.

• Drive debate during the 2012 congressional and presidential campaigns.

"It's going to be enormous," said Kenneth Janda, a professor emeritus of political science at Northwestern University.

Congress is playing the fanfare, with a largely symbolic House health-care vote Thursday to repeal the law's provision for a 15-member independent commission to help control Medicare costs.

Theatrically speaking, the House's curtain-raising action on the eve of the court cases enabled lawmakers to rehearse their arguments and emphasize the high stakes.

Amicus briefs

Across Capitol Hill, the history making is apparent in everything from the extraordinary 100-plus so-called "friend of the court" amicus briefs filed in the cases to the unusually speedy same-day release of the audiotapes of the arguments. Several dozen talk-radio hosts will be broadcasting from temporary studios near the court. Senators had urged the court, unsuccessfully, to televise the proceedings.

The six hours of arguments will begin Monday morning and conclude around noon Wednesday. They'll address four key legal questions.

Simply put: Can Congress compel individuals to buy insurance? Can Congress pressure states to expand Medicaid coverage by threatening to withhold funds? Can the rest of the law survive if one part is struck down? And, from the get-go, are lawsuits challenging the measure prematurely?

The Supreme Court won't delve into every nook of the law formally called the Patient Protection and Affordable Care Act. The House approved the bill in March 2010 in a narrow 219-212 vote; the Senate in a 60-39 vote.

No Republicans voted for it in either body.

As the health-care bill was debated in 2009 and 2010, the United States faced three big hurdles related to health care, noted Amitabh Chandra, an economist and professor of public policy at Harvard University.

These were to insure the uninsured; improve the quality of care; and cut costs by reducing unwarranted, unnecessary care.

"The law only deals with the first challenge," Chandra said. "It does little on quality and even less on cost. It begins the conversation."

The law contains hundreds of provisions, some uncontested, such as the requirement that insurance companies offer coverage for children up to age 26 on their parents' insurance.

Health-care exchanges, or marketplaces, will allow consumers to comparison shop for coverage once they're fully up and running in 2014.

Starting that year, the individual mandate also requires most people to obtain health insurance and imposes annual financial penalties, starting at $95, on those who don't. The law pressures states to expand Medicaid eligibility to those with incomes of up to 133 percent of the federal poverty level; if states don't, they'll lose federal money.

Premature lawsuits?

The legal conversation Monday will begin with the basics: Are the lawsuits premature?

Early on, the Obama administration said the legal challenges violated the Anti-Injunction Act. This generally obscure 1867 law blocks court actions challenging new taxes until those taxes have taken effect. The Obama administration originally deployed this technical argument but lost. Now, President Obama and his opponents agree the health-care lawsuits may be addressed on their merits.

The Supreme Court has assigned an independent attorney to make the Anti-Injunction Act argument. Few court observers expect this kick-it-down-the-road case to prevail.

The individual mandate is the hottest topic. It's the latest version of a question that's several centuries old: How much power does the Constitution grant Congress?

The Constitution's Commerce Clause authorizes Congress to "regulate commerce ... among the several states." Separately, the Constitution permits Congress to pass laws that are "necessary and proper" to exercise its authority.

Since the 1930s, the Supreme Court had interpreted these clauses liberally. But in more recent cases, such as one in 1995 that struck down a federal law regulating guns near schools, conservative majorities have stressed congressional limits.

"If you can say to somebody, 'Your failure to purchase health insurance is within the role of the federal government,' why can't the federal government say you have to go to the gym or you have to eat your broccoli?" then-Sen. George LeMieux, R-Fla., said during Senate debate on the measure.

In response, the Obama administration stresses that the law is all about regulating commerce, because of the substantial effect health care has on the national economy. The uninsured consumed $116 billion worth of health care in 2008 that they didn't pay for, officials estimate. Health-care providers shift those costs onto insurance companies, which generally pass them on to the insured.

"The act breaks this cycle through a comprehensive framework of economic regulation and incentives that will improve the functioning of the national market for health care," Solicitor General Donald Verrilli Jr. argued in a brief.

If the court strikes down the individual mandate, justices also must decide whether it can be severed from the rest of the law or the entire law must sink along with it.

Naturally, the Obama administration wants the rest of the health-care law to survive even if the mandate is struck down. Opponents do not.

Practically speaking, a conservative-minded court might hesitate to gut an entire law that's already taking effect. Insurance companies, for instance, already have extended family coverage to some 2.5 million young adults younger than 26.

The final challenge — questioning the Medicaid expansion, which is set for Wednesday — caught by surprise many who hadn't expected the court to go so far. States argue that they're being forced to spend money they don't have to expand coverage. Congress, they say, can't simply coerce them with the threat of withholding billions of dollars.

This could be huge, going well beyond health care. In the past, for instance, the court has allowed Congress to withhold highway funds from states that set legal drinking ages younger than 21. If the Medicaid expansion falls, future Congresses will lose clout.

"It has not received the same kind of attention as the individual mandate, but it is extremely important," Jane Perkins, the legal director of the National Health Law Program, an advocacy group for low-income individuals, said of the Medicaid case.