President Barack Obama, seeking to break the congressional impasse over legislation to avert a Jan. 1 tax increase, called House Speaker John Boehner Wednesday to urge approval of a two-month extension of current tax rates and promised to negotiate a longer extension in the new year.

Mr. Boehner (R., Ohio) showed no immediate sign of giving ground, and instead urged Mr. Obama to lean on Senate Democrats to enter into another round of negotiations before the end of this year.

The exchange came as Mr. Boehner and House Republicans were coming under mounting pressure from fellow Republicans to end a standoff that critics said was damaging the GOP by stalling popular legislation to prevent a Jan. 1 increase in payroll taxes, a cut-off of extended unemployment benefits and a steep drop in Medicare payments to doctors.