By Lisa Lambert and Sarah N. Lynch

WASHINGTON (Reuters) - The U.S. Senate could vote as early as Monday on confirming President Donald Trump's pick for education secretary, Betsy DeVos, with the political parties potentially entering a standoff requiring Vice President Mike Pence to act as tie-breaker.

On Friday morning, the Senate voted 52 to 48 on a procedural measure paving the way to the final confirmation vote, which the education committee chairman, Senator Lamar Alexander, said will happen early in the week.

DeVos, a billionaire philanthropist and charter-schools advocate, has faced unusually fierce opposition for a role that rarely receives congressional debate or public notice.

After her confirmation hearing, where DeVos seemed ill-equipped to discuss public education issues and suggested allowing guns at schools to fend off bear attacks, voters flooded Capitol Hill with calls and emails to block her nomination.

Senators Susan Collins and Lisa Murkowski have said they will not vote for her, the first Republicans to break party ranks and vote against one of Trump's cabinet nominees.

If one more Republican sides with Democrats against her nomination, DeVos will become only the 10th cabinet nominee in U.S. history rejected by Congress.

Voting margins are so thin that Pence, as head of the Senate, may have to cast a tie-breaking vote.

The Senate's top Democrat, Charles Schumer, pressed Republicans to consider voting against her over the weekend.

"The nominee for the secretary of education is one of the worst nominees that has ever been brought before this body for a cabinet position," he said on the Senate floor. "Sometimes loyalty to a new president demands a bit too much."

Alexander, a former education secretary, is confident that DeVos will ultimately be approved. On the Senate floor he said she would be excellent in the role. Republicans see DeVos as a champion of low-income children and local control of education.

"I would argue that she has been among the forefront of the leaders...for the most successful reform of the last 30 years to change and improve public education, and that would be the public charter schools," he said.

Democrats worry DeVos' support for charters, which operate independently of school districts and are frequently run by corporations, means she wants to undermine public schools.

They also have expressed dismay about her refusal to pledge to uphold rules on sexual assault, for-profit colleges and fair access to disabled students, as well as potential conflicts of interest with her investments.

(Reporting by Lisa Lambert; Editing by Chizu Nomiyama and Bernadette Baum)