WASHINGTON – A federal appeals court struck down a pillar of President Obama’s national health care law on Friday, ruling that Congress does not have the power to require all Americans to buy health insurance and setting the stage for a Supreme Court decision ahead of the 2012 elections.

The 2-1 decision is a victory for Republican leaders in 26 states, including Maine Gov. Paul LePage, who had challenged the law last year, testing whether the signature accomplishment of Obama’s presidency will stand.

The Atlanta-based judges echoed the complaint that the mandate represents an “unprecedented” expansion of federal power.

“The individual mandate is breathtaking in its expansive scope,” the two judges of the 11th Circuit Court of Appeals wrote in their 207-page majority opinion.

Even during the Great Depression or World War II, “Congress never sought to require the purchase of wheat or war bonds, force a higher savings rate or greater consumption of American goods,” they said. While Congress may regulate those who buy insurance, it may not regulate those who “have not entered the insurance market and have no intention of doing so.”

LePage said the ruling illustrates that the federal government’s powers are not limitless. He said it’s a step forward in “upholding our liberties” under the Constitution.

About 50 million Americans lack basic health insurance. As a result, hospitals and taxpayers pay about $43 billion a year to cover the costs of those who are treated but cannot pay.

Many health care experts believe an insurance mandate is crucial to not only controlling this cost shift, but also guaranteeing that all Americans can get insurance.

Without such a requirement, consumers would be able to wait until they were sick to buy insurance. That, in turn, would push up premiums.

However, the mandate galvanized GOP opposition to the law and helped to fuel the tea party movement.

Senate Minority Leader Mitch McConnell, R-Ky., said the ruling “only strengthens and adds more momentum to the efforts of those of us who are working to repeal.”

The White House minimized the opinion, citing the divided rulings by multiple federal courts around the country.

“Today’s ruling is one of many decisions on the Affordable Care Act that we will see in the weeks and months ahead,” Stephanie Cutter, assistant to the president, wrote in a blog posting.

The ruling was not a total victory for the challengers. The appeals court rejected the states’ claim that Congress went too far by expanding the Medicaid program for low-income Americans. The judges also agreed the rest of the health care law can stand.

The Atlanta-based court has a conservative reputation and had been seen as the best forum for those challenging the law. The majority was made up Chief Judge Joel Dubina, an appointee of President George H.W. Bush, and Judge Frank Hull, a female appointee of President Clinton. The dissenter, Judge Stanley Marcus, was a Clinton appointee.

In dissent, Marcus said judges have a duty to act with “caution, restraint and great humility” and uphold laws enacted by elected lawmakers.

“At bottom, Congress rationally concluded that the uninsured’s consumption of health care services shifts enormous costs unto others … and the individual mandate directly addresses this cost-shifting problem,” Marcus said in dissent.

In June, the Obama administration prevailed before the federal appellate court in Cincinnati, which in a split opinion ruled that the mandate represented a constitutional exercise of Congress’ authority to regulate commerce.

The administration can appeal Friday’s decision directly to the Supreme Court. If an appeal petition is filed during the fall, the justices are likely to hear the case early next year and rule by late June.

Striking down the mandate could have dramatic consequences if insurance premiums surge, as many experts fear.

That could put more pressure on the federal treasury because millions of Americans are expected to qualify for federal subsidies starting in 2014 to help buy insurance.