Tauscher, who represents a California district, has a record of introducing arms control and counter proliferation legislation and has campaigned for greater oversight of the US Missile Defense Agency.

She said in a statement in March, after details of her impending appointment emerged, that she decided to take the job of under secretary of state for arms control and international security after a period of "soul searching."

"Keeping nuclear weapons out of the hands of terrorists, making sure other countries do not obtain them and, one day, I hope, ridding the world of these terrible weapons, has become my passion and, I hope, my life?s work," she said.

Nancy Pelosi, speaker of the US House of Representatives, said Obama and Secretary of State Hillary Clinton would benefit greatly from Tauscher's "talent, experience, and immense knowledge" and called for speedy Senate confirmation of her appointment.

Also on Tuesday, Obama formally nominated Andrew Shapiro, a long-time key Clinton foreign policy advisor, as assistant secretary of state for political-military affairs.

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