WASHINGTON (CNN) -- In one of the most highly anticipated Supreme Court hearings in years, the justices on Tuesday offered sharply divided views on the controversial individual mandate provision at the heart of the 2010 federal health care reform law.
The fate of the individual mandate -- requiring most Americans to purchase health insurance by 2014 or face a financial penalty -- may be in jeopardy, and perhaps with it the entire law's other 450 or so sections, based on tough questions of the government by the court's conservative majority.
"Most of the times, the questions that are asked at oral arguments are a pretty good predictor of where things are going to go," said Jeffrey Toobin, CNN's senior legal analyst, who added he thinks the health care reform law is in "grave danger."
Neither the justices nor the lawyers arguing before them mentioned "Obamacare"-- as opponents have labeled the law pushed through Congress by Democrats and President Barack Obama -- or the president by name.
But the court seemed fully aware of the landmark consequences of their eventual rulings.
"Those who don't participate in health care make it more expensive for everyone else," said Justice Ruth Bader Ginsburg, in support of the law. "It is not your free choice" to stay out of the market for life, she said.
Younger, mostly health people who would be the "subsidizers will become the subsidized" when they grow older, added Justice Elena Kagan.
However, Justice Anthony Kennedy said that the federal government "is telling an individual he has the obligation he must act" and purchase insurance.
"That threatens to change the relationship between the government and the individual in a profound way," Kennedy said.
If Congress could regulate health care in the name of commerce, added Chief Justice John Roberts, "all bets are off" on a range of areas subject to federal oversight.
To Toobin, the court's four liberal justices -- Ginsburg, Kagan, Sonia Sotomayor and Stephen Breyer -- were clearly supportive of the law's constitutionality, while conservative justices Samuel Alito and Antonin Scalia appeared certain to rule against the law.
With Justice Clarence Thomas also considered certain to vote on the conservative side, the issue would be decided by the remaining votes of Kennedy and Roberts, Toobin said.
Kennedy, who is considered the swing vote on the divided court, asked tough questions about the mandate and appeared likely to oppose its constitutionality, Toobin said, meaning that the usually conservative Roberts may be the best hope of liberals for the law to be upheld.
Tuesday's argument was the biggest of the high court's three-day marathon this week examining the limits of congressional authority. It was part legal seminar, part history lesson, with politics sprinkled throughout.
Dueling protests outside the court reflected the partisan nature of health care debate.
Rep. Michele Bachmann of Minnesota, who failed in her bid for the Republican presidential nomination to take on Obama in November, told tea party supporters near the Supreme Court building that the issue is freedom for individuals to decide their health care needs.
"If the federal government can tell you, when you are not doing anything, that you must do something, then the federal government can tell you anything," Bachmann said, later adding a call for the Supreme Court to declare the mandate unconstitutional.
She noted that two years after being signed into law, the health care measure "has not united our country."
"It has divided us more than ever," Bachmann said, gesturing to nearby pro-reform counter-protesters. "Look around you."
Earlier, a cancer patient told a news conference by supporters of the law that it saved her life.
"Because President Obama signed the Affordable Care Act, I get to keep my house, I won't go bankrupt, my kids are going to get to go to college, and I am going to live," Spike Dolomite Ward said to cheers.
The nine-member bench kept Tuesday's two hours of arguments focused on the constitutional and policy implications.
At issue: May the federal government, under the Constitution's commerce clause, regulate economic "inactivity"? Three federal appeals courts have found the Affordable Care Act to be constitutional, while another has said it is not, labeling it "breathtaking in its expansive scope."
That "circuit split" all but assured that the Supreme Court would step in and decide the matter.
A coalition of 26 states, led by Florida, argues individuals cannot be forced to buy insurance, a "product" they may neither want nor need.
The Justice Department has countered that since every American will need medical care at some point in their lives, individuals do not "choose" to participate in the health care market.
Federal officials cite 2008 figures of $43 billion in uncompensated costs from the millions of uninsured people who receive health services -- costs that are shifted first to insurance companies and then passed on to consumers.
A CNN/ORC International poll released Monday indicated that the health care law is growing in popularity, especially among independent voters, but half of those questioned still oppose it. However, while most opponents of the measure believe it goes too far, some who disapprove think it's not liberal enough.
The poll found an almost even split on the individual mandate, with 47% in favor and 51% opposed, a gap within the survey's margin of error. According to the survey, a gender gap exists on the issue, with 58% of men opposing the mandate while 53% of women support it.
In addition, a stark partisan divide exists on the issue, with 71% of Democrats favoring the mandate while 78% of Republicans oppose it. Among independents, 56% oppose the provision.
The opposing sides do not even agree on what the mandate -- known as the "buy in" or "minimum coverage" provision -- was designed to accomplish.
Supporters see it as a way to spread health care costs among a larger pool of individuals, ensuring affordable, quality medical care. They say regulating commerce and the economy has long been a federal prerogative.
Opponents see fundamental constitutional violations, such as an intrusion into a citizen's personal life and an intrusion in long-held state power.
Most individuals would be covered under the mandate, except for those whose religious beliefs would conflict, as well as illegal aliens and inmates.
It would fall on insurance companies to inform the government of those covered under their health policies. The case is Department of Health and Human Services v. Florida (11-398).
"This is such an extraordinary case and why you have so many states that have joined in this one lawsuit," said attorney Paul Clement, who argued for the states this week. "These issues are really central to whether the federal government can really regulate anything it wants to, or whether there are some things that only the state governments can regulate."
However, supporters of the law say the federal government had to get involved.
"Congress thought it necessary to regulate the nearly 20% of our nation's economy that makes up the health care industry and to make sure insurance companies did not discriminate against people with pre-existing conditions, for example, and pass the minimum coverage provision. That is squarely within Congress' authority," said Elizabeth Wydra, chief counsel of the Constitutional Accountability Center. "No one says that there is a right to freeload off one's neighbors when you decide not to choose health care."
It is the individual mandate that has sparked the most controversy. It requires nearly every American to purchase some level of insurance or face a tax penalty of up to about $700 a year.
On Monday, the justices quickly bored of the dense legal argument presented on whether the individual mandate was a "tax," which would put off consideration of the larger constitutional questions for another few years.
Few on the bench seemed eager to embrace that go-slow approach, and some justices began asking questions about Tuesday's argument on the individual mandate.
That shows where the court's real focus lies, knowing their ruling on this key question will have enormous legal, social and political implications. The ruling is expected by late June.
CNN's Tom Cohen and Paul Steinhauser contributed to this report.