The Senate on Tuesday unanimously confirmed CIA Director Leon Panetta to serve as the next secretary of defense.

Panetta, who was tapped by President Obama in April to succeed Robert M. Gates as head of the Pentagon, is expected to assume his new post early next month. Gates had earlier announced that he planned to step down this year after serving as defense secretary for 4½ years.

The Senate’s 100 to 0 confirmation of Panetta comes at a time of wide-ranging changes to Obama’s national security team. On Thursday, Gen. David H. Petraeus, whom Obama has named as his choice to succeed Panetta at the CIA, will face a confirmation hearing before the Senate Select Intelligence Committee. The same day, the Senate Foreign Relations Committee is set to vote on the nomination of Ryan C. Crocker, a former U.S. ambassador to Iraq, to succeed Karl W. Eikenberry as ambassador to Afghanistan.

The confirmation of Panetta comes on the eve of Obama’s expected announcement that the United States will begin its drawdown of forces from Afghanistan next month. The president is expected to announce that 30,000 “surge” troops will be withdrawn from the country by the end of next year.

On the floor Tuesday, senators from both parties spoke out in support of Panetta as they did during his confirmation hearing in early June, one month after the mission that killed Osama bin Laden in Abbottabad, Pakistan. Several members referenced that mission in their remarks praising Panetta on Tuesday.

“I believe when history looks back . . . one of the most important roles played in this effort to prepare the way for those courageous SEALS was the steady leadership of Leon Panetta at the head of the CIA,” Sen. Jack Reed (D-R.I.) said.

Senate Armed Services Committee Chairman Carl Levin (D-Mich.) added later: “President Obama turned to Director Panetta to personally oversee the manhunt for Osama bin Laden and the awe-inspiring operation that brought an end to al-Qaeda’s murderous leader and provided a measure of relief to the families and friends who have suffered since September 11th, 2001.”

“The raid on the bin Laden compound,” Levin said, “epitomizes the way in which the CIA and the Defense Department are finally working together to support each other in counterterrorism operations, and Director Panetta deserves credit for this close coordination.”

Several senators also praised Panetta’s tenure as head of the Office of Management and Budget under President Bill Clinton, noting that the Defense Department will be subject to many of the same budget battles facing the rest of the federal government at a time of record national debt.

Sen. John McCain (R-Ariz.) also spoke in support of Panetta’s nomination, as did Sen. Lindsey O. Graham (R-S.C.). As Graham was talking, one of the Senate’s most outspoken Democrats, Sen. Charles E. Schumer (N.Y.), interrupted to get in a word of praise for Panetta.

“That’s about as bipartisan as you’re going to get,” Graham said, laughing, as Schumer finished his remarks.