BERLIN—U.S. Treasury Secretary Timothy Geithner said Tuesday that he was impressed by the steps European leaders are taking toward "enormously difficult" reforms in the wake of the euro zone's debt crisis, adding he was confident that they would help stabilize the currency bloc.

"I come away from these discussions convinced as I have been for some time that the European authorities understand what it's going to take and how to make sure that they maintain the right balance between support for the reform programs that are...