A leading Republican senator said Sunday that he would block Senate confirmations of President Obama’s nominees to lead the C.I.A. and the Department of Defense unless he was given more information on the attack on the United States compound in Benghazi, Libya, last year.

Senator Lindsey Graham of South Carolina, a vocal critic of the administration’s handling of the attack, said he would use a Senate custom known as a hold to stall the nominations of John O. Brennan as C.I.A. director and former Senator Chuck Hagel as Pentagon chief until the White House gave him a full description of Mr. Obama’s actions during the attack on Sept. 11.

“What did he do that night?” Mr. Graham asked during an appearance on CBS’s “Face the Nation,” suggesting that the president could have intervened to manage the crisis personally.

“That’s not unfair,” Mr. Graham added. “The families need to know.”

Ambassador J. Christopher Stevens and three other Americans were killed when heavily armed Islamic extremist militants stormed and burned the compound.