If confirmed, the 55-year-old appeals court judge would replace retiring Justice David Souter on the nine-member court that is the final arbiter of the US Constitution and often confronts volatile political and social issues, including gun control and abortion.
Over at least four days of hearings, the panel will hear from people like former FBI director Louis Freeh, who mentored Sotomayor, and Linda Chavez, a conservative activist.
President Barack Obama, who nominated Sotomayor for the key post, telephoned her on Sunday to wish her good luck and congratulated her for having met with 89 senators ahead of the hearings.
"The president expressed his confidence that Judge Sotomayor would be confirmed to serve as a justice on the Supreme Court for many years to come," a White House statement said.
Experts say the confirmation fight may be more fizzle than sizzle, noting that the Democrats have, at least on paper, the 60 votes needed to overrun any Republican efforts to use Senate delaying tactics to stymie the nomination.
"I suspect she will be confirmed, but I would hope that it does not turn into a partisan fight for the good of the court," Democratic Senator Patrick Leahy, chairman of the Senate Judiciary Committee, said on CBS television.
"She has a track record. She has shown to be a mainstream judge. You don't have to guess what kind of a judge she's going to be."
But Republicans have served notice they plan to put up a fight, giving one of their 14 witness slots to one of the white firefighters whose claim of racial discrimination Sotomayor rejected -- only to have the Supreme Court reverse her ruling in late June.
That could buttress a central Republican argument that Sotomayor cannot be trusted to separate her personal and political beliefs and decide cases based on their legal merit.
Republican Senator Jeff Sessions raised doubts on CBS whether Sotomayor could be objective, saying Supreme Court justices need to "do equal justice to the rich and poor alike."
"She has advocated a view that suggests that your personal experiences, even prejudices... it's expected that they would influence a decision you make. Which is a blow, I think, at the very ideal of American justice."
But Senator Jon Kyl, reported to be leading the Republican strategy for the confirmation hearings, vowed on ABC that Sotomayor would get a fair hearing.
"The strategy is to be as thorough as we can in examining her record, what she has said, and to conduct the hearings in a fair, impartial, and thorough way, and then make our decisions."
Privately Republicans say they worry about hurting the party with Hispanic voters, who went 67 percent to Obama and 31 percent to his Republican rival, Senator John McCain, in November 2008.
Hispanics, the fastest-growing US minority with a major presence in key states such as Florida and battlegrounds like New Mexico and Arizona, have increasingly flexed their national political clout.
A July 1 Rasmussen poll however found that the initial favorable public reaction to Sotomayor appeared to be waning slightly. Thirty-seven percent of respondents believed she should be confirmed and 39 percent were against.
Obama and his allies however have touted Sotomayor's decades-long legal career, past support from hard-line Republicans and her "well qualified" rating from the American Bar Association.
Sotomayor's personal rise from a poor childhood in the Bronx in New York to the pinnacle of US justice mirrors Obama's own storybook ascent to power.
Upon announcing her nomination, the US president declared that Sotomayor could boast a "brilliant legal career" and "the wisdom accumulated from an inspiring life's journey."
The list of Democratic witnesses includes former Major League Baseball pitcher David Cone, sure to highlight a ruling by Sotomayor that ended the 1994-95 Major League Baseball strike.
Princeton-educated Sotomayor, who hails from a Puerto Rican family, would be the second woman currently on the court, alongside Justice Ruth Bader Ginsburg.
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