Alan Krueger, the top White House economist, said Tuesday that extending the payroll tax cut as President Barack Obama proposed would strengthen the U.S. economy and not doing so would cause ``severe drag.''

``This is a critical time for the economy and I think it's a time when the economy could use more medicine to strengthen and sustain the recovery,'' Krueger told a news briefing.

``Extending the payroll tax cut will strengthen the recovery,'' he said, saying the proposal that Republicans in Congress are cool to would also provide a buffer against shocks that may be coming including from Europe.

(Reporting by Laura MacInnis and Andy Sullivan, Editing by Sandra Maler)