Senior White House Adviser David Axelrod said Sunday that he expects a public insurance option to make it into a final health care overhaul bill despite a promise from one key lawmaker who opposes such a program.

But Sen. Joseph I. Lieberman , I-Conn., who has complicated the fate of that provision by pledging to support a filibuster to end debate on a Senate bill that includes a public option, renewed the threat and defended his position as principled.

The dispute over the public option remains key to the broader debate on health care reform, even as House Democratic leaders last week unveiled a bill featuring the provision and Senate Majority Leader Harry Reid , D-Nev., pledged to include a version of it in his chamber's measure. The question now centers on whether...