As the Treasury Department prepares to float a plan today calling for a new blueprint to regulate Wall Street, curiosity is swirling around the man who will likely play a key role in implementing the proposals: Timothy Geithner, the baby-faced 46-year-old president of the Federal Reserve Bank of New York.

A former civil servant who shuns the spotlight, Mr. Geithner has made but a single speech so far this year, despite orchestrating some of the Fed’s most radical recent strategies to help stave off a recession, including facilitating the sale of Bear Stearns to JPMorgan Chase & Co. and opening the discount lending window to noncommercial banks. With these programs, Mr. Geithner has made it clear he isn’t afraid to take bold, unprecedented action in the face of fiscal disaster.

“Many people can discuss a problem to death, but there aren’t many people who are prepared to take responsibility for choosing a course of action,” a former Treasury secretary, Lawrence Summers, said. “What stands out about Tim is he is on the one hand very thoughtful, but on the other hand perfectly comfortable with acting.”

Mr. Geithner surprised Wall Street in 2003 when he took on the role of New York Fed chief — one of the world’s most important economic positions — despite having almost no market experience. From the very beginning of his career, though, he has shown he isn’t easily intimidated.

After graduating from Dartmouth College and earning a master’s degree in international economics and East Asian studies from Johns Hopkins University, Mr. Geithner took a job researching a book for Henry Kissinger.

“I thought he was extremely intelligent,” the former secretary of state recalled, adding that he still has the papers Mr. Geithner wrote for him. Although quiet and unassuming, the young man wasn’t afraid to speak his mind to the Nobel laureate. “He doesn’t try to walk into a room and take it over,” Mr. Kissinger said. “He prevails with the power of his argument.” At 26, Mr. Geithner went to work at the Treasury Department, where Mr. Summers said he was struck by his keen intellect and grace under pressure.

“He’s very calm, he doesn’t get rattled, he doesn’t start yelling,” said Mr. Summers, who hired Mr. Geithner as his special assistant in 1988 and promoted him three times, helping him move to undersecretary for international affairs from mid-level staffer. “It was just obvious that he stood apart from other civil servants in terms of the clarity of his thought, his ability to get things done, his understanding of policy problems.”

Mr. Geithner, who declined to be interviewed for this article, became an integral part of a close team that worked to deal with the 1994 crisis involving the Mexican peso, the Asian financial crisis, and the collapse of the hedge fund Long Term Capital Management. Along the way, he demonstrated not only a level head, but a consuming hunger for new sources of information, according to Ted Truman, a Federal Reserve alum who worked for Mr. Geithner at Treasury. “His intellectual style actively pursues a range of alternative views,” Mr. Truman said. “He reaches out to people for good information and advice and views wherever he can find them.”

At Federal Reserve Bank luncheons, Mr. Geithner prefers to listen than to talk, peppering guests at his table with questions, according to a vice chairman and chief legal officer at Lehman Brothers, Thomas Russo. “He’s constantly probing, trying to understand people’s views,” Mr. Russo said. “Tim is anything but in an ivory tower.”

After a brief stint at the International Monetary Fund, Mr. Geithner was tapped to head the Federal Reserve Bank of New York. The role made him vice chairman of the Federal Open Market Committee and the only one of 12 bank presidents with a permanent vote on the panel, which sets the level of the all-important federal funds rate.

“If Bernanke is Eisenhower, then Geithner is General Patton,” a professor of economics at New York University, Mark Gertler, said, referring to the Fed chairman, Ben Bernanke. Mr. Geithner is “out there on the front lines dealing directly with financial institutions.”

The choice of Mr. Geithner surprised Wall Street because of his lack of private sector financial experience, Mr. Gertler said, but Mr. Geithner’s crisis-management skills made him a good fit for the role. “He has an excellent understanding of what’s going on,” Mr. Gertler said.

In recent weeks, Mr. Geithner, along with Mr. Bernanke and the Treasury secretary, Henry Paulson, has introduced innovative solutions for handling the current financial maelstrom. “He has been in a real leadership role in prescribing remedies that are somewhat outside the box,” Mr. Russo said.

Today, Mr. Paulson is expected to make a policy speech outlining a new blueprint for regulating Wall Street. Among the proposals he will suggest, according to an article in the New York Times, is to provide the Fed with the authority to examine the books of investment banks or other financial institutions when their activities threaten the stability of the market. In addition, the plan will call for consolidating some financial regulators, including combining the various state-run insurance regulators and merging the Commodity Futures Trading Commission with the Securities and Exchange Commission.

The new blueprint follows several unorthodox programs the Fed has recently instituted, including opening for the first time since the 1930s its so-called discount window to noncommercial banks and offering JPMorgan a $29 billion line of credit to help facilitate its acquisition of Bear Stearns. Because the financial institutions that are now borrowing from the Fed’s discount window are largely based in New York, and because the city is where JPMorgan and Bear Stearns are based, Mr. Geithner’s New York Fed has played a central role in designing these novel approaches.

Mr. Russo calls the Fed’s decision to lend directly to banks “a brilliant move,” adding: “It was very important to send a message of liquidity.”

Others, including Senate Democrats calling for an investigation of the Bear Stearns deal, have criticized the Fed’s recent actions as a bailout for Wall Street fat cats at taxpayers’ expense.

While Mr. Summers said he might have made some decisions a bit differently, he’s sure of one thing: Mr. Geithner’s competence in his role at the central bank. “I sleep better at night knowing he’s there,” Mr. Summers said.