WASHINGTON, (Reuters) - A key U.S. Senate committee  endorsed a sweeping healthcare overhaul yesterday, gaining the  support of an influential Republican and delivering President  Barack Obama a victory on his top domestic priority.

The Democratic-controlled Senate Finance Committee approved  the measure by 14-9, with Senator Olympia Snowe becoming the  first Republican in Congress to back a healthcare reform bill.

“Today we reached a critical milestone in our effort to  reform our healthcare system,” said Obama, who warned there  were still big challenges ahead for healthcare reform.

The bill, the last of five pending health measures to clear  a committee in Congress, will be merged with the Senate health  panel’s version for a floor vote.

Snowe, who had been courted by Obama and his fellow  Democrats, said she backed the plan with reservations and could  not guarantee her continued support as the overhaul advances.

“My vote today is my vote today. It doesn’t forecast what  my vote will be tomorrow,” Snowe said.

Health insurer companies stocks fell on fears the reform  was gaining steam and would hurt profits if it passed. The S&P  Managed Health Care index of large health insurers was down 1.9  percent.

“Support for Democratic healthcare legislation by Senator  Snowe is a critical development, which definitively shifts the  political balance in Democrats’ favor,” said healthcare  equities analyst Avik Roy.