WASHINGTON  Caught between a pivotal industry ally and the protests of Congressional Democrats, the Obama administration on Friday backed away from what drug industry lobbyists had said this week was a firm White House promise to exclude from a proposed health care overhaul the possibility of allowing the government to negotiate lower drug prices under Medicare.

The reversal underscored the delicate balancing act the White House has pursued in its strategy of negotiating behind-the-scenes deals to win industry support without alienating liberal supporters on Capitol Hill.

Pressed by drug industry lobbyists, a White House deputy chief of staff, Jim Messina, confirmed in an e-mail message on Wednesday that the White House shared the drug lobbyists’ interpretation of the deal: that any health care overhaul would not include allowing direct government negotiation of drug prices or require certain additional price rebates. Since Wednesday, other representatives of the White House had also stood by Mr. Messina’s statement as well.

After reading reports about Mr. Messina’s e-mail message, House and Senate Democrats loudly protested that they would not be bound by any such agreement to remove clauses allowing government negotiation of drug prices under Medicare  something Democrats have sought for years.