WASHINGTON, Nov 30 (Reuters) - A slowing recovery and a surging pandemic mean the United States is entering a “challenging” few months, with the potential deployment of a vaccine still facing the hurdles of production and mass distribution before its impact on the economy becomes clear, Fed chair Jerome Powell said on Monday. “The rise in new COVID-19 cases, both here and abroad, is concerning and could prove challenging for the next few months,” Powell said in remarks prepared for delivery to a congressional hearing on Tuesday morning. “Recent news on the vaccine front is very positive for the medium term. For now, significant challenges and uncertainties remain, including timing, production and distribution, and efficacy across different groups. It remains difficult to assess the timing and scope of the economic implications of these developments with any degree of confidence.” (Reporting by Howard Schneider in Washington and Ann Saphir in Berkeley, Calif. Editing by Matthew Lewis)