The White House scrambled Thursday to tamp down a burst of anxiety among liberals worried that President Barack Obama would agree to extend Bush-era tax cuts for the wealthiest Americans.

Liberal economists and activists were responding to comments senior White House adviser David Axelrod made to the Huffington Post, which reported that Mr. Axelrod said the administration was ready to accept a temporary extension of all such tax cuts, which are due to expire at the end of the year.

Mr....