The White House security procedures in place during last week’s state dinner had been used at times during past administrations without problems, the Secret Service director said Thursday as he tried to explain how a Virginia couple managed to talk their way into one of the most heavily guarded buildings in the world.

A contrite Mark Sullivan told the House Homeland Security Committee that the breakdown was an isolated incident and not an institutional failure.

“I believe it’s due just to poor judgment,” Sullivan told lawmakers, adding that three uniformed agents had been placed on paid administrative leave while investigators look into how Tareq and Michaele Salahi managed to attend a state dinner for the Indian prime minister without being on the guest list.

The pair of aspiring reality television stars -- as well as White House Social Secretary Desiree Rogers -- declined to testify Thursday. That left Sullivan as the sole witness.

Committee Chairman Bennie Thompson (D-Miss.) emphasized that the matter was about “real-world threats to the nation.” That didn’t stop him from playing to cameras, however, by placing two name cards in front of empty chairs when it was the Salahis’ scheduled turn to speak.

Thompson said he would seek subpoenas for their testimony, but would not do the same for Rogers, despite Republican objections.

“Ms. Rogers is not a central figure in this security matter,” Thompson said.

Rogers’ office has come under scrutiny for not posting staff members at security checkpoints -- a practice that’s been used to support Secret Service agents at other state dinners, but not all White House functions, Sullivan said.

His agents have handled the guest list before, he said, although he did not know whether they had done so at a state dinner. Last week, the agents were instructed to notify a supervisor and the White House social office if the name of someone seeking entry did not show up on the list, he said. That did not happen.

“This is the first time that we had a breakdown based on our people accepting” responsibility for the guest list, Sullivan said.

The decision not to post White House staff at the checkpoints -- in addition to Secret Service -- was a joint recommendation agreed upon before the event, he said.

The White House has since said it will post staff at each gate as a matter of policy.

The incident has spawned more than a week of scrutiny of White House security procedures, with Sullivan repeatedly accepting blame.

But he pushed back Thursday when Rep. Eleanor Holmes Norton (D- D.C.) suggested that the event may not have been properly staffed given reports of a rise in threats against President Obama.

Sullivan said that the number of threats against the nation’s first black president was now “at the same level it was” during the two previous administrations.

In an interview Thursday with USA Today, Obama said that he was “100% confident” in his protection, though he acknowledged the system didn’t work as planned.

kathleen.hennessey@ latimes.com