WASHINGTON, Oct 21 (Reuters) - The U.S. economy grew at a "nontrivial" rate in the third quarter and probably would again in the current period, White House economic adviser Lawrence Summers told Reuters in an interview on Wednesday.
"There's really no doubt that the third quarter registered growth, and growth at a nontrivial rate, and every expectation that the fourth quarter will do the same," Summers said at the Reuters Washington Summit.
Summers, who heads the White House's National Economic Council, acknowledged that unemployment would remain elevated for some time, and said there was not yet a basis for confidently forecasting very rapid growth.
"So economic slack remains a central problem," he said.
He said the question of what will propel economic growth throughout the expansion was a "crucial one. But that is always the case at the beginning of expansions." (For summit blog: http://blogs.reuters.com/summits/) (Reporting by Caren Bohan, Jeff Mason and Simon Denyer; Writing by Emily Kaiser, Editing by Anthony Boadle)