On a party-line vote of 51-47, the Senate rejected a Republican measure to rescind the law that aims to provide more than 30 million uninsured Americans with medical coverage while requiring nearly all to be insured or pay a fine. Sixty votes were needed to clear a procedural hurdle against repeal.

Senate Majority Leader Harry Reid scoffed at Republican efforts, saying: "They want to replace patients' rights with insurance companies' power. They want to replace health with sickness. They want to replace the promise of tomorrow with the pain of yesterday."

Senate Republican leader Mitch McConnell countered: "The case against this bill is more compelling every day. Everything we learn tells us it was a bad idea. That it should be repealed and replaced. The courts say so. The American people say so."

The Senate voted two days after a federal judge struck down the 2010 law as unconstitutional, a ruling the Obama administration promptly announced it would appeal.

The Republican-led House of Representatives, in keeping a campaign vow, voted to repeal the healthcare law last month.

Senate rejection of the repeal effort means the law's fate will likely be decided by court challenges and eventually the U.S. Supreme Court, a process that could extend into next year.

A federal judge in Florida on Monday ruled that Congress overstepped its authority in requiring that nearly all Americans obtain insurance or pay a fine.

Ramifications of the new law for the health sector have been widespread, affecting Aetna Inc, WellPoint Inc and other health insurers as well as drugmakers, device companies and hospitals.

States, struggling to balance their books in the aftermath of the recent economic downturn, also face higher costs for the Medicaid health program for the poor.

Democrats say the law benefits people who had been unable to obtain coverage and ought to be maintained and improved.

HEARING HELD ON LAW'S CONSTITUTIONALITY

The Senate Judiciary Committee on Wednesday held the first congressional hearing on the constitutionality of the law.

Republican Senator Charles Grassley, a one-time participant in drafting the law who later withdrew from negotiations, said it was unclear what the Supreme Court may decide.

"What is clear is that if this law is constitutional, Congress can make Americans buy anything that Congress wants," Grassley said.

Democrats say they believe the Supreme Court will ultimately decide in favor of the law.

Assistant Senate Democratic leader Dick Durbin said a number of landmark laws, including the 1964 Civil Rights Act and 1935 Social Security retirement program, ran into trouble in lower courts before being upheld by the Supreme Court.

"I believe the same will happen with the Affordable Care Act," Durbin said of the law being challenged in many courts.

"For those keeping score, 12 federal district court judges have dismissed challenges to the law, two have found the law to be constitutional and two have found the opposite," Durbin said.

While the Senate blocked appeal, it approved a measure to rescind a provision that Democrats and Republicans agreed saddled small businesses with excessive paperwork.

Republicans vowed to keep pushing to roll back other provisions.

McConnell said: "We think this is just the beginning. This issue is still ahead of us and we will be going back at it in a variety of different ways."

(Editing by Peter Cooney)