“One of the bigger worries I have is we’ve had all this hoopla and nothing’s going to happen,” she said at a coffee shop here recently on a rare quiet afternoon. “But it might also be helpful to us, because it’s going to be hard for any opposition to be steadily pushing for seven years.”

The federal health care law has complicated Vermont’s plans, requiring the state to first create a health insurance exchange to help residents shop for coverage by 2014. The state would then need a federal waiver to trade its exchange for a government-run system.

Dr. Richter said she embraced the idea of a single-payer system as a young doctor in Buffalo, where many of her patients put off crucial treatments because they were uninsured. As a medical student, she saw a patient with a life-threatening heart infection caused by an infected tooth that had gone untreated because he lacked dental insurance.

“He was in the hospital for six weeks, and I was like, ‘This makes no sense,’ ” she said.

She went to a meeting of Physicians for a National Health Program, a group that advocates for a national single-payer system, and started researching the concept. Before long she became a vocal advocate, even becoming president of the physicians’ group, and moved to Vermont.

John McClaughry, a former Republican state senator who is against the new law, said Dr. Richter meant well but did not understand the “long-term damage” it would wreak. In particular, he said the law would drive away businesses that did not want to help pay for it.

“She’ll tell you that putting in single-payer will attract businesses from all over the place,” said Mr. McClaughry, vice president of the Ethan Allen Institute, a conservative research group. “I don’t think she has any appreciation of business decisions at all.”

Since moving with her husband and two sons to a rambling old house within view of the State House, Dr. Richter has given about 400 talks on the single-payer concept, tutored lawmakers in the State House cafeteria and testified before the Legislature more times than she can remember. Once, she presented a printout of all the insurance companies her small practice in Cambridge had billed over five years.