An historic reform of US health care has passed a key hurdle when Senate Democrats narrowly mustered the 60 votes needed to open formal debate on President Barack Obama's top domestic policy initiative.

The 100-seat chamber's two independents joined all 58 Democrats -- including two waverers who declared their intentions just hours earlier -- to launch what is expected to be a weeks-long fight over opposition from 39 of 40 Republicans.

Republican Senator George Voinovich of Ohio did not vote. "The President is gratified that the Senate has acted to begin consideration of health insurance reform legislation," White House spokesman Robert Gibbs said.

"Tonight's historic vote brings us one step closer to ending insurance company abuses, reining in spiraling health care costs, providing stability and security to those with health insurance, and extending quality health coverage to those who lack it. The President looks forward to a thorough and productive debate," Gibbs added.

Yesterday's Democratic win came after moderate lawmakers Mary Landrieu of Louisiana and Blanche Lincoln of Arkansas agreed to move the issue into formal debate, but while warning they would insist on changes to core provisions in the 2,074-page plan before voting for final passage.

The legislation would extend coverage to some 31 million Americans who currently lack it and restrict insurance companies' ability to deny coverage to clients.