WASHINGTON – Supreme Court nominee Elena Kagan confronted her Senate Judiciary Committee critics Monday, telling them that her experience and her broad philosophy will bring impartiality and “a commitment to principle” to the court.

“The Supreme Court has the responsibility of ensuring that our government never oversteps its proper bounds or violates the rights of individuals,” Kagan said in her 12-minute opening statement. “But the court must also recognize the limits on itself and respect the choices made by the American people.”

Nonetheless, Republicans challenged the readiness of the 50-year-old Kagan to serve on the court, with the GOP’s senior Judiciary Committee member, Sen. Jeff Sessions of Alabama, saying he had “serious questions about this nomination.”

Kagan, the solicitor general and a former Harvard Law School dean, has had limited courtroom experience. But Democrats, led by Judiciary Committee Chairman Sen. Patrick Leahy of Vermont, said her resume suggested that she’d be an excellent justice.

“I believe that fair-minded people will find her judicial philosophy well within the legal mainstream,” he said.

Since Democrats control 58 Senate seats, Kagan is expected to win confirmation to replace 90-year-old Justice John Paul Stevens, who is retiring.

She began Monday at the Oval Office, where President Obama wished her well, and then sat in the vast Senate hearing room as each of the 19 committee members offered glimpses of their views.

The room was crowded but lacked the anticipation and drama that have characterized similar hearings. The public lines to get in weren’t as long, and there were empty seats in the media gallery.

Kagan was introduced by Massachusetts Sens. John Kerry, a Democrat, and Scott Brown, a Republican, who called her “an impressive and pleasant individual.”

Kagan then sat alone at the long witness table. She recalled her parents, who “lived the American dream,” including a mother whose family was from Ukraine and who “didn’t speak a word of English until she went to school” and became a “legendary teacher.”

She talked about the court appointment as the “honor of a lifetime,” and addressed concerns about her resume.

“I’ve led a school whose faculty and students examine and discuss and debate every aspect of our law and legal system,” she said.

Throughout the opening day of what’s expected to be a weeklong confrontation, Republicans and Democrats alike were maneuvering for advantage. In an unusual and aggressive touch designed to help shape early news coverage, the White House released excerpts from Kagan’s opening statement several hours before she was to deliver it.

Kagan was to begin answering questions from committee members today, and most made it clear that they see her nomination – any nomination, for that matter – as another chapter in the struggle for ideological control of the court.

Sessions offered a list of concerns reaching back to Kagan’s college thesis on socialism and to a stint in the Clinton White House, where “she was perhaps the key person who convinced President Clinton to change his mind from supporting to opposing legislation” to ban late-term abortions.

Republicans plan to question her about military recruiters at Harvard and her opposition to the Pentagon’s “don’t ask, don’t tell” policy banning gays and lesbians from openly serving.

“We don’t have any substantive evidence to demonstrate your ability to transition from a legal scholar and political operative to a fair and impartial jurist,” said Sen. Charles Grassley, R-Iowa.

Democrats argued otherwise, saying Kagan’s real-world experience was a plus.

“You’ve had a lot of practical experience reaching out to people who hold very different beliefs,” said Sen. Amy Klobuchar, D-Minn., “and that’s increasingly important on a very divided Supreme Court.”

Democrats are two seats short of the number needed in the Senate to cut off debate, but filibusters against nominees are rare, and some Republicans signaled they could support Kagan.

“At the end of the day, I think the qualification test will be met,” said Sen. Lindsey Graham, R-S.C., who backed Obama nominee Sonia Sotomayor last year. “Whether or not activism can be parked is up to you.”

Kagan’s appointment isn’t expected to shift the court’s ideological balance dramatically, although justices stress that every new member changes the court in unpredictable ways.

In her opening statement, Kagan almost seemed to issue a warning: Don’t try to pin me down.

“I will make no pledges this week other than this one: that if confirmed … I will do my best to consider every case impartially, modestly, with commitment to principle and in accordance with law.”