Clinton responded: "The president-elect has said repeatedly it is unacceptable. It is going to be United States policy to pursue diplomacy — with all of its (tools) — to do everything we can to prevent Iran from becoming a nuclear weapon state. As I also said, no option is off the table."

She said the new administration would pursue a broader approach to the problem of Islamic extremism in Afghanistan and Pakistan.

"We must also actively pursue a strategy of smart power in the Middle East that addresses the security needs of Israel and the legitimate political and economic aspirations of the Palestinians; that effectively challenges Iran to end its nuclear weapons program and sponsorship of terror, and persuades both Iran and Syria to abandon their dangerous behavior and become constructive regional actors; that strengthens our relationships with Egypt, Jordan, Saudi Arabia, other Arab states, with Turkey, and with our partners in the Gulf to involve them in securing a lasting peace in the region. "

Clinton also promised to push for stronger U.S. alliances around the globe.

"America cannot solve the most pressing problems on our own," Clinton said, "and the world cannot solve them without America."

She credited Secretary of Defense Robert Gates with stimulating debate about the role of diplomacy and other civilian institutions' role in fighting the global war on terror, endorsing his call for providing the State Department with more resources and a bigger budget.

She assured the committee that if confirmed, the State Department "will be firing on all cylinders" — applying pressure when needed and looking for opportunities to advancing U.S. interests.

"Today's security threats cannot be addressed in isolation," Clinton said. "Smart power requires reaching out to both friends and adversaries, to bolster old alliances and to forge new ones. That means strengthening the alliances that have stood the test of time — especially with our NATO partners and our allies in Asia."

Clinton spoke in a clear, unhurried voice and looked at ease as she read a long introductory statement. She sat alone at a small, black-draped desk, with daughter Chelsea and a retinue of advisers behind her. Her husband was not present. Obama spokesman Tommy Vietor said the former president was watching the hearing elsewhere with his wife's mother.

"President Clinton wanted to make sure the attention was focused on Sen. Clinton," Vietor said. "They will be together as a family later today."

The Senate hearing room was packed with ambassadors, current and former diplomats, supporters and aides sitting cheek by jowl. Dozens of photographers ringed Clinton as she spoke.

Clinton appeared set to sail smoothly toward confirmation, despite concerns among some lawmakers that the global fundraising of her husband could pose ethical conflicts for her as secretary of state.

The Senate is also holding four confirmation hearings Tuesday for other Obama choices for Cabinet and top White House positions. Appearing will be Peter Orszag, his choice to head the Office of Management and Budget, and Robert Nabors II, for deputy director of OMB; New York housing official Shaun Donovan, to be secretary of housing and urban development; Steven Chu, to head the Energy Department; and Arne Duncan, as education secretary.