The Supreme Court opened its historic review of the national health-care overhaul Monday with an indication that it will be able to decide the constitutional question of whether Congress exceeded its powers despite arguments that the challenge was brought too soon.

The court began the first of three days of oral arguments on the 2010 law by examining a statute that keeps courts from hearing tax challenges before they go into effect. But the justices’ questions indicated skepticism that the penalties prescribed for those who do not buy health insurance by 2014 amount to taxes under the 1867 law forbidding tax challenges.

The court on Tuesday will hear arguments about the so-called “individual mandate” that is at the heart of the health-care law.

The court had asked Washington lawyer Robert A. Long to present the argument that the obscure 19th-century law — the Anti-Injunction Act — meant that lawsuits brought by 26 states and a private business organization were premature. Long said the court’s precedents showed that the statute should keep any court from hearing the case until someone actually had to pay a penalty on his or her 2015 income tax returns for not purchasing health insurance.

Long said the “pay first, litigate later rule” could not be waived except by Congress, and it made no such provision in the Patient Protection and Affordable Care Act. He said the penalties called for in the act should be considered the same as taxes because of the way they are collected.

A panel of the U.S. Court of Appeals for the 4th Circuit agreed that the Anti-Injunction Act barred a consideration of the merits of the health-care overhaul. But Long was appointed to present that legal argument because neither the Obama administration nor the law’s challengers agree with it.

Several of the justices pushed back against Long’s argument.

Just because the penalty is “being collected in the same manner of a tax doesn’t automatically mean it’s a tax,” said Justice Stephen G. Breyer, “particularly since the purpose of the Anti-Injunction Act is to prevent interference with the revenue stream.” This legal challenge does not interfere with revenue collection, Breyer added.

Justice Antonin Scalia appeared to agree. As a matter of principle, he said, the courts should not be deprived of jurisdiction in cases unless the reasoning is very clear. “I find it hard to think this is clear, whatever else it is,” Scalia said.

Solicitor General Donald B. Verrilli Jr., representing the government, said the justices should proceed to deciding the merits of the case.

“This case presents issues of great moment, and the Anti-Injunction Act does not bar the court’s consideration of those issues,” Verrilli said.

Verrilli had to be careful, though. While he insisted that the penalty is not a tax for Anti-Injunction Act purposes, he is expected to argue as the case proceeds that Congress is within its authority to pass the health-care law in part because of its ability to tax.

“Today you are arguing that the penalty is not a tax,” said Justice Samuel A. Alito Jr. “Tomorrow you will be back and arguing that the penalty is a tax.”

Verrilli said what Congress called the penalty was important for purposes of the Anti-Injunction Act, but not to the greater question of its taxing authority.

The act adopted in 1867 states that “no suit for the purpose of restraining the assessment or collection of any tax shall be maintained in any court by any person.” It was designed to make sure that the flow of tax collection necessary to keep the government running was not disrupted by lawsuits.

As the review began, hundreds of supporters and opponents of the health-care law marched outside the Supreme Court. The demonstrations highlighted the contentiousness of President Obama’s signature domestic initiative, which was signed into law two years ago and continues to galvanize his opponents.

Former senator Rick Santorum (Pa.), a contender for the Republican presidential nomination, made an appearance Monday on the steps of the Supreme Court to campaign against the law — and blast GOP front-runner Mitt Romney. Santorum vowed that, if elected, he would repeal “Obamacare,” which he described as the central issue of his campaign.

“If you really want Obamacare repealed, there’s only one person who can make that happen,” Santorum told reporters. “Obviously, I don’t believe that Obamacare is constitutional,” he added in response to a question.

In the early stages of litigation over the health-care law, the Obama administration agreed that the Anti-Injunction Act barred an immediate constitutional decision. But it dropped that argument and told the Supreme Court that the “penalty” for failure to secure health insurance is not a “tax” for Anti-Injunction Act purposes.

The 26 states challenging the Affordable Care Act (ACA), as well as the private organization and individuals who are party to the challenge, also want the court to act now.

“The purpose of this lawsuit is to challenge a requirement — a federal requirement to buy health insurance,” Washington lawyer Gregory G. Katsas told the court. “That requirement itself is not a tax. And for that reason alone, we think the Anti-Injunction Act doesn’t apply.”

Besides the 4th Circuit panel, the view that the Anti-Injunction Act forecloses a ruling at this time was endorsed by Circuit Judge Brett M. Kavanaugh, an influential conservative member of the U.S. Court of Appeals for the D.C. Circuit.

“Waiting to decide might mean never having to decide,” keeping the courts out of the political fray, Kava­naugh wrote. If there is no change in the law between now and 2015, he said, the constitutional decision could be made then.