It was a big political discussion in a very small room.

“Medicare for all” got its first congressional hearing on Tuesday, albeit in one of the House’s tightest meeting rooms, in an area of the Capitol off limits to the scores of people who assembled in Washington to show support.

The idea of a single government health care system for all Americans has been treated with extreme caution by the Democratic leadership, which has stressed more modest improvements to the current health law. On Tuesday, Speaker Nancy Pelosi’s office was pointing to the bills moving through the House Judiciary Committee that could lower the prices of prescription drugs.

Yet here was Ms. Pelosi herself, escorting a supporter of Medicare for all, Ady Barkan, to the House Rules Committee meeting. Mr. Barkan, who has long advocated health care expansion, has the degenerative neural disease amyotrophic lateral sclerosis and used a computer to help him speak. He proved a powerful presence.

“We have so little time together, and yet our system forces us to waste it with bills and bureaucracy,” he told the committee in his opening statement, noting that the fast progress of his disease had impressed upon him the urgency of reform. “That is why I am here today, urging you to build a more rational, fair, efficient and effective system.”