ATLANTA — A federal appeals panel has struck down the core component of President Obama’s health care overhaul, shifting the question of whether Americans can be required to buy health insurance a step closer to the Supreme Court.

A divided three-judge panel of the 11th Circuit Court of Appeals ruled that Congress overstepped its authority when it passed the so-called individual mandate, the first such decision by a federal appeals court.

Administration officials said they are confident the ruling will not stand. The Justice Department can ask the full 11th Circuit to review the panel’s ruling and is expected to appeal to the Supreme Court.

The 207-page opinion and 84-page dissent made clear that views of the Obama administration’s signature health care reform law have increasingly hardened as voices from each side present familiar arguments and precedents to buttress their opposing ­conclusions.

The opinion said Congress had broad power to deal with the problems of the uninsured “but what Congress cannot do is mandate that individuals enter into contracts with private insurance companies for the purchase of an expensive product from the time they are born until the time they die.”

The Obama administration is now 1-1 in federal appeals courts in defending the law, and the rulings have defied partisan lines. Judge Frank Hull, who was appointed by President Clinton, was part of the 11th Circuit’s 2-1 majority that most recently ruled against the mandate. Conversely, a George W. Bush appointee on the 6th Circuit upheld it in an earlier ruling.

The 11th Circuit Court didn’t consider the mandate along the same lines as other courts have. Generally, the two sides have battled over whether the insurance requirement regulates “economic activity,” which Congress has the power to do under the Constitution, or instead compels people to participate in an economic activity, as opponents of the law argue.

For the most part, the 11th Circuit bypassed that distinction, although it emphasized that the mandate is ­unprecedented.

Obama has championed the individual mandate as a major accomplishment of his presidency and as a way to try to slow the costs of health care while expanding health insurance coverage to the approximately 30 million Americans who lack it.