With his nerdy eyeglasses, square jaw and unfashionable fealty to dark suits in a business-casual city, Benjamin Rosenfield is the Clark Kent of San Francisco City Hall.

Rosenfield, the city’s earnest young controller, holds the possibly impossible job of keeping the city solvent in the face of an estimated $380 million budget deficit and a bitter political battle over ballooning employee costs. But with his almost messianic belief that honest numbers can pave the way for a “right” answer to the city’s budget crisis, he may yet emerge as Superman.

Rosenfield, 37, is a public servant in the old sense of the term, and sui generis at San Francisco’s rough-and-tumble City Hall. Everyone trusts him, and he is regarded as incapable of lying or proffering a number tweaked for political purposes.

With such a yawning gap between the city’s financial obligations and its revenue, there is only so much that any executive-branch bureaucrat, however capable and politically skilled, can do. Rosenfield is not a policy maker and cannot unilaterally decree cuts or raise revenue. His role is to work behind the scenes, as a financial consigliere, using his deep knowledge of how the city’s finances actually work to prod the mayor and supervisors in directions that will produce significant results.

Rosenfield is “a true believer that government needs to do good,” said Edward M. Harrington, his former boss and predecessor as controller, who is now head of the San Francisco Public Utilities Commission.

“Not that people in government lie, but he can actually, physically, not have that happen,” Harrington said.

When his fellow city executives put forth financial untruths, Harrington said, “Ben gets physically uncomfortable. He fidgets; his face turns red. He has a physical reaction when someone is not telling the truth. It just doesn’t sit with him.”

That is not to say that Rosenfield is naïve. The numbers may not “lie,” but he is more aware than anyone else how malleable they can be.

Take the current debate raging around pension reform. With a union-city working group toiling on a consensus proposal, and Jeff Adachi, the public defender, readying another contentious ballot initiative, Rosenfield is striving to produce numbers for all parties that will provide rare and bracing clarity.

“Better information, numbers without bias to all participants, leads to better outcomes,” he said in an interview.

He cited, for example, a seemingly hard-knuckle proposal for capping pensions for city workers at about $100,000. Having studied the matter, Rosenfield says this would yield just $1 million in savings by 2016. With the city’s pension bill forecast to be $674 million by that year, such initiatives are all but meaningless for a numbers guy, and suggest that the policy makers need to do a lot better.

Rosenfield’s journey to his present post was serendipitous. Raised in Chicago, he cut his teeth in city politics in notoriously corrupt Providence, R.I., while he was still an undergraduate at Brown. As a 23-year-old, he wrote a letter to San Francisco’s mayor at the time, Willie L. Brown Jr., asking for an internship. Four years later, he was the mayor’s budget director. In 2008, he was appointed to a 10-year term as controller.

In his quiet, nonconfrontational way, Rosenfield insists almost as a point of personal honor that San Francisco is in no danger of bankruptcy. When asked about Mayor Edwin Lee’s recent comment that rising employee costs, if unchecked, could tilt the city into insolvency, Rosenfield shook his head in dismay.

“There is no way that San Francisco goes bankrupt,” he said. “As costs increase, services are reduced. The debt service will be paid.”

That services for residents could, in theory, be reduced to zero to cover debt and retiree costs is not Rosenfield’s chief worry. His job is to keep San Francisco Inc. solvent and its debt-rating high.

It would seem to be a thankless grind. But Rosenfield views his job with Clark Kent-like equanimity: “I find the current situation intellectually interesting.”

But he is human, after all, and at the end of the day he goes home to his wife and two young daughters at their house in the city. So he is not immune to the worries that dog everyone with an economic stake in the city’s economic viability. Because right now, things do look grim.

“As a San Franciscan,” he acknowledges, “it is alarming.”

For Clark Kent, that’s pretty bleak stuff.

This article also appears in the Bay Area edition of The New York Times.