He relaxes by playing the harmonica (he is in a band called the Capitol Offenses); his rendition of “Amazing Grace” at a friend’s funeral “had everybody in tears,” said Gov. James E. Doyle of Wisconsin. His aides are fiercely loyal. “People around him put up with his peculiarities,” said Scott Lilly, who spent nearly 30 years with Mr. Obey, “because they really do like him.”

In Congress, Mr. Obey has spent decades championing federal spending on health, education and social programs, an agenda rooted in his Catholic faith, which, he has said, demands that he try to “make this an equal society for everybody.” A campaign poster of Franklin Roosevelt  “my hero,” he says  looks over his shoulder in his sun-streaked Capitol office, where a window offers testimony to his power: a view of the Washington monument.

“The main thing for Obey is his longstanding commitment to the domestic policies that he cares about, especially when the competition for the money is a war he disagrees with,” said David Canon, a professor of political science at the University of Wisconsin.

So at a time when Congress “has been lectured ad nauseam” about paying for a health care overhaul without raising the deficit, Mr. Obey says the same standard must be applied to the war. He knows he will have difficulty getting his surtax passed; Ms. Pelosi opposes it. But he will have little trouble getting Democrats to scrutinize the president’s war budget request.

“His questions are very similar to those within our caucus: Do we have credible partners in Afghanistan and Pakistan? What is the mission? What’s the risk?” said Representative Rosa DeLauro, a Connecticut Democrat and member of the House leadership. She sees the surtax as Mr. Obey’s way of forcing the nation to think about “shared sacrifice,” adding, “He’s a smart, savvy legislator.”

But Mr. Obey is also a loyal Democrat, which puts him in a ticklish position. Before he proposed the surtax, he called Mr. Nabors to give the president a heads-up. That resulted in the president’s call. Mr. Obey used the conversation to ask the president if he had seen a documentary by the public television journalist Bill Moyers featuring archival audiotapes of President Lyndon B. Johnson wrestling with escalating the Vietnam War.

“It is stunning,” he remembers telling Mr. Obama, “to listen to Johnson talk to Dick Russell, the conservative old wise head in the Senate from Georgia  it is terrible, gut-wrenching to listen to them both say, ‘Well, we know this is damn near a fool’s errand, but we don’t have any choice.’ ”