Gibbs said on NBC's "Meet the Press" there is "no doubt there are enough seats in play that could cause Republicans to gain control," and Democratic prospects depended on running strong campaigns.
The comment raised some eyebrows among political analysts. At the daily White House briefing Tuesday, reporters asked Gibbs if he regretted the remark.
"Well, I think I said that there were enough seats in play, and I think that's true," he said.
"I also said I thought that the election was going to be about choices. I think those choices are more -- those choices are clearer every day," Gibbs said.
Noting Republican comments on the gulf oil spill, the recession and unemployment, Gibbs said voters will make "value judgments" in November.
"I think we will retain the House," he said. "I was asked if there were enough seats in play, and I think there are."