WASHINGTON — The defeat of two conservative House Democrats by more liberal opponents in Tuesday’s Pennsylvania primary illustrates the strong hold the new health care law still has over committed Democratic voters and foreshadows an even more polarized Congress next year in the aftermath of the latest round of redistricting.

Representatives Jason Altmire and Tim Holden both lost in primaries to opponents who joined together with activist groups to pummel the veteran lawmakers over the opposition to the new health care law and climate change legislation — positions they had used to their advantage in the past to show their independence from President Obama and the Democratic Party.

“A lot of us thought of his record as his strength,” said Hugh M. Reiley, the chairman of the Schuylkill County Democratic Party, referring to Mr. Holden. “He was not falling prey to all that party bickering. He was able to reach across the aisle.”