WASHINGTON — “Our Dr. Rice” is the friendly moniker Democrats in the foreign policy community often bestow on Susan Rice.

The reference to the Secretary Rice now running the State Department is usually made in jest, but the comparison could carry significantly more weight if Senator Obama, who on Saturday won the South Carolina primary and today is poised to win the endorsement of Senator Kennedy, becomes America’s next president.

As a senior foreign policy adviser to Mr. Obama, Susan Rice, 43, has taken a leading role in helping to shape the freshman Illinois senator’s vision for the world, building on a bond forged in part by their shared — and outspoken — opposition to the war in Iraq.

An assistant secretary of state under President Clinton, Ms. Rice also served as a senior adviser on the Kerry-Edwards campaign in 2004, and she is likely to be on the short list for a top position in an Obama administration, perhaps in the same role Condoleezza Rice served during President Bush’s first term: national security adviser.

The Rices are not related, but as two prominent African American women in a field long dominated by white men, the comparison is as natural as it is superficial.

“We thought our Dr. Rice was a lot more sensible than their Dr. Rice,” quipped James Rubin, a former State department spokesman who worked with Susan Rice on the Kerry campaign but who is now an informal adviser to Senator Clinton. Susan Rice said she has seen Secretary Rice occasionally over the years but does not know her well. They share a link to Stanford University — Susan Rice studied there as an undergraduate in the 1980s while Condoleezza Rice taught as a professor. Like Mr. Obama, Ms. Rice has long been a fierce critic of the Bush administration’s foreign policy, and she does not look to Secretary Rice as a role model.

“I don’t select role models on the basis of race and gender,” she said in a telephone interview. She praised the two previous secretaries of state, Madeleine Albright and Colin Powell, but she said the jury was still out on Secretary Rice’s tenure.

Susan Rice grew up in Washington, D.C., the daughter of an economist who served as a governor of the Federal Reserve, Emmett Rice, and an education policy scholar, Lois Rice. She won a Rhodes scholarship and later earned a doctorate in international relations from Oxford University after graduating from Stanford in 1986. Ms. Rice joined the Clinton White House in 1993 and rose quickly. Within two years she was a senior director for African affairs on the National Security Council. In 1997, President Clinton appointed her assistant secretary of state for Africa, overseeing more than 40 countries and 5,000 foreign service officials.

She first met Mr. Obama when he was a Senate candidate in 2004, and she became a resource and adviser for him the following year when he took a seat on the Foreign Relations Committee. The two discussed a range of issues, from Iraq to nuclear non-proliferation to counterterrorism.

“I was attracted to him in the very beginning as someone who was extraordinarily intelligent, thoughtful, and had a remarkably broad and deep grasp of the key foreign policy challenges of the day,” she said. Ms. Rice said she was drawn to him in part because of his early and vocal opposition to the Iraq war. She had also spoken out on the war before the American invasion, and she said she respected Mr. Obama for making “the same unpopular choice I had made,” despite what she described as a “huge amount of pressure in Washington to go along with or support the war.”

Since the end of the Clinton administration, Ms. Rice has written often about a range of issues, and particularly the genocide in Darfur. She has pushed a much more aggressive American position on Sudan, including the possible use of military force in 2005 and 2006. She has backed off that position to some extent, saying efforts should now be focused on beefing up and deploying a joint United Nations-African Union peacekeeping force, which the Sudanese government has resisted. “I think the challenge is somewhat different today, and the prescription at the moment is somewhat different,” she said.

As one of several former Clinton administration officials who have decamped to Mr. Obama, Ms. Rice joins a former national security adviser to President Clinton, Anthony Lake, in the Illinois senator’s inner circle of foreign policy advisers. She characterized the move as a relatively easy decision, given the similarity in their policy views and the fact that she had gotten to know him well while she had had little contact with the Clintons in recent years.

“Supporting Senator Obama was a clear choice for me,” she said, “but it was never a choice against Senator Clinton or President Clinton, whom I have long respected.”

Still, she has not held back in criticizing Mrs. Clinton during the campaign, and a few of her former colleagues privately seethed at comments she made minimizing the New York senator’s role in foreign policy as first lady.

In the interview, Ms. Rice said Mr. Obama had offered a more substantive foreign policy platform than Mrs. Clinton, who she said had “revealed relatively little” about her approach to foreign policy and national security during the campaign. Citing Mrs. Clinton’s article in the journal Foreign Affairs, she said Mr. Obama’s vision was more forward-looking and, in a message that has emerged as a dominant theme in the campaign, that Mrs. Clinton’s goal of “restoring” American power was rooted in the past.

“If you read that article, it’s hard to discern a vision of a new American leadership beyond just getting out from under the Bush years,” Ms. Rice said. Associates describe Ms. Rice as hard charging but disciplined, a manager who brings a laser-like focus and blunt-spoken clarity to tasks large and small.

“She’s a tenacious battler for the policies and principles she believes in,” a member of the Obama foreign policy team who worked with Ms. Rice in the Clinton administration, John Prendergast, said. “She really will not quit.”

Those who have worked with Ms. Rice said her style could occasionally ruffle feathers, but a member of Mr. Obama’s foreign policy inner circle, Major General Scott Gration, said that while she was a “take-charge person,” she was well-liked. “She accomplishes a task while building a team,” General Gration said, adding that she often runs Mr. Obama’s foreign policy meetings along with Mr. Lake and Denis McDonough, a former top aide to Senator Daschle. “She’s a great administrator,” he said. The Obama campaign has at times made use of her as a surrogate spokeswoman; the day of the Iowa caucuses, she appeared on Fox News Channel to speak about the campaign in general, not about specific foreign policy issues.

Ms. Rice, a fellow at the Brookings Institution, is married to an ABC News producer, Ian Cameron, with whom she has two young children.”My leadership style is one that aims to be inclusive and to mobilize and encourage people to give their best,” she said. “I plead guilty as charged to wanting to move and get things done and occasionally being impatient.”

As for her role under a possible President Obama, she demurs, saying she is focused on getting the senator elected. “I am not focused on what I do thereafter,” she said.