The HIG team was deployed after the Times Square bombing attempt this month, administration officials said this week.
Blair also told Congress that Abdulmutallab continued to provide helpful information to investigators at a time when authorities had hoped to keep the bomber's cooperation secret. With that information divulged, FBI Director Robert Mueller confirmed at the same hearing that Abdulmutallab was cooperating.
Blair was the first Obama administration official to describe the deadly shooting rampage at Fort Hood, Texas, last fall as an act of homegrown extremism. The administration had previously been reluctant to call the suspect, an Army psychiatrist, a homegrown terrorist or extremist.
By law, the principal deputy director of national intelligence, David Gompert, becomes the acting director until the Senate confirms the president's nominee, Sen. Dianne Feinstein, D-Calif., said.
Rep. Pete Hoekstra, the top Republican on the House Intelligence Committee, called Blair a consummate public servant.
"I had high hopes for his willingness to work with Congress on a bipartisan basis to ensure that America's intelligence professional had the tools, resources and authorities they need to help protect our homeland," Hoekstra said Thursday.
Some Republican lawmakers have criticized the Obama administration for not keeping them in the loop on key intelligence matters, often singling out Brennan as being too secretive.