For years, Clinton has asserted she made a difference in achieving peace in Northern Ireland, but some critics said her role was more symbolic than substantive.

In a December 2007 interview with ABC News, Clinton said: "In just the last few weeks, the new leaders of the Northern Ireland government, Dr. Ian Paisley and Martin McGuinness, made a special effort to see me. Why? Because I helped in that process, not just standing by and witnessing, but actually getting my hands into it, creating opportunities for people on both sides of the sectarian divide to come together."

As a member of the Senate Armed Services Committee she visited Iraq and other countries and is well versed in the diplomatic fallout from the unpopular Iraq war and Bush administration policies in the global hunt for terrorists.

She differed with Obama over the war during their primary contest. Clinton was forced to repeatedly defend her 2002 Senate vote authorizing the U.S. invasion of Iraq, but security improvements in Iraq now mean the two substantially agree on what to do from here.

Obama still vows to withdraw U.S. troops from combat in 16 months or less. But top aides quietly point to escape clauses he has sprinkled into documents and interviews.

Numerous outside observers think he is likely to take a more deliberate approach to disengagement and keep diplomatic pressure on the unsteady Iraq government to do more for itself.

James Carafano, a national security expert at the conservative Heritage Foundation, calls Clinton a realist on Iraq and other issues.

"She's not pollyanna-ish about the world," he said, and could be effective in promoting U.S. interests.

"You could do a lot worse. She's obviously well-known, she's got a strong personality, she'd be a good negotiator."

Likewise, foreign policy hawk Danielle Pletka at the American Enterprise Institute calls Clinton's drive and discipline a good match for the job. "She's a grown-up," Pletka said.

The symbolism of a woman and former rival in one of the most visible jobs in American government is probably the least reason Obama might choose her, and says little about how well she would perform, said Michael O'Hanlon, defense and foreign policy analyst at the center-left Brookings Institution.

"Obama is already a symbol," O'Hanlon said. "The reason to consider her is because she's so darn smart, because she is competent, because he knows her and he believes they can have honest disagreements as well as cooperate on most issues when they do agree."