Doug Mills/The New York Times

The White House delivered a strong message to Wall Street on Thursday, taking the unusual step of choosing two former prosecutors as top financial regulators.

But translating that message into action will not be easy, given the complexities of the market and Wall Street’s aggressive nature.

At a short White House ceremony, President Obama named Mary Jo White, the first female United States attorney in Manhattan, to run the Securities and Exchange Commission. Mr. Obama also renominated Richard Cordray as the director of the Consumer Financial Protection Bureau, a position he has held for the last year under a temporary recess appointment without Senate approval.

With the appointments, the president showed a renewed resolve to hold Wall Street accountable for wrongdoing, extolling his candidates’ records as prosecutors.

Ms. White spent more than a decade as a top federal prosecutor in New York City, overseeing the prosecution of the crime boss John Gotti and those responsible for the 1993 World Trade Center bombing. As an Ohio prosecutor, Mr. Cordray filed lawsuits against Bank of America and the American International Group.

“It’s not enough to change the law,” Mr. Obama said. “We also need cops on the beat to enforce the law.”

Still, Ms. White and Mr. Cordray face their own challenges.

While Ms. White, 65, is best known as an aggressive prosecutor, she also built a lucrative legal practice defending Wall Street executives, a potential concern for consumer advocates. And she lacks experience in the financial minutiae central to a regulatory role.

Mr. Cordray, 53, presents another potential problem for the White House. The Senate last year declined to confirm him in the face of Republican and Wall Street opposition to the newly created consumer bureau. Several Republicans on Thursday again voiced their concerns.

“There’s absolutely no excuse for the Senate to wait any longer to confirm him,” Mr. Obama said.

Both Midwestern natives, Ms. White and Mr. Cordray arrived in Washington as outsiders. A five-time “Jeopardy” champion from Ohio, Mr. Cordray became the consumer bureau’s enforcement chief after losing re-election for state attorney general. As Ohio’s top prosecutor, he became known as the Midwestern sheriff of Wall Street.

Ms. White, who was born in Kansas City, Mo., changed career paths after graduating with a master’s degree in psychology. She obtained a law degree from Columbia University in 1974, and a few years later, began her first stint as a federal prosecutor in Manhattan.

She ultimately became the United States attorney in Manhattan, earning a reputation as a tenacious prosecutor with an independent streak. Ms. White embraced the often-repeated joke that her office was the United States attorney for the “sovereign,” rather than Southern, district of New York.

In 1997, aides to Manhattan District Attorney Robert M. Morgenthau accused her of trying to thwart a state insider trading investigation by allowing a defendant charged by the district attorney’s office to plead guilty to federal charges. Doing so effectively ended Mr. Morgenthau’s case, but Ms. White was unapologetic. “To prosecute such crimes under only state law diminishes their seriousness,” she said at the time.

As the chief federal prosecutor in Manhattan, Ms. White pursued white-collar crime and Wall Street fraud. She secured a $340 million fine against Daiwa Bank for illegally covering up trading losses and other crimes.

She distinguished her career with a series of terrorism cases. She supervised the original investigation into Osama bin Laden and Al Qaeda, and oversaw six major trials, including those stemming from the 1993 World Trade Center bombing and a plot to blow up New York landmarks.

Patrick J. Fitzgerald, the former United States attorney in Chicago who previously worked under Ms. White, called her “a force of nature.”

She also trained a generation of federal prosecutors. Two former assistants became high-level S.E.C. officials: Robert S. Khuzami, the departing enforcement chief, and George S. Canellos, his deputy. Preet Bharara, the current United States attorney in Manhattan, whom Ms. White hired in 1999, emphasized her “legendary work ethic,” citing her 1 a.m. e-mail dispatches. Her philosophy, Mr. Bharara said, was that prosecuting wrongdoing was “not just about earning notches on your belt.”

While former employees described her as “no nonsense,” she was often spotted sipping a Bud Light at a weekly social gathering for junior prosecutors. And despite being barely 5 feet tall, she also was an exuberant point guard in a local lawyers’ basketball league, and once arrived at a tennis match on a red motorcycle, while Helen Reddy’s “I Am Woman” blared loudly.

With her prosecutorial victories and independent political status, Ms. White is expected to receive broad support on Capitol Hill. Senator Charles E. Schumer of New York joined a chorus of Democratic enthusiasm on Thursday, declaring that Ms. White was a “tough-as-nails prosecutor.”

But she could face questions about her command of Wall Street arcana.

Regulatory chiefs are often market experts or academics. If confirmed, Ms. White will succeed Elisse B. Walter, a longtime S.E.C. official, who took over as chairwoman after Mary L. Schapiro stepped down as the agency’s leader in December. Ms. Schapiro, a seasoned policy maker and specialist in market structure, overhauled the agency after it was blamed for missing the warning signs of the financial crisis. Ms. White, in contrast, built her career on the law-and-order side of the securities industry, with just a brief stint as a director of the Nasdaq.

The gaps in her résumé could complicate Ms. White’s agenda in the face of fierce Wall Street lobbying. Under the next chairman, the agency must write dozens of rules to carry out the Dodd-Frank act, a regulatory overhaul passed in response to the crisis. The agency also must grapple with the increasingly complex markets and rapid-fire trading that dominate Wall Street.

People close to the S.E.C. note, however, that her husband, John W. White, is a veteran of the agency. From 2006 through 2008, he was head of the S.E.C.’s division of corporation finance.

Ms. Schapiro also argued that Ms. White’s outsider status could inject new life into the agency. “Nobody comes in an expert across the board,” Ms. Schapiro said. “A fresh look on some of these policy issues might be exactly what we need.”

Ms. White could face additional questions about her career, a revolving door in and out of government. In private practice, she defended some of Wall Street’s biggest names, including Kenneth D. Lewis, a former chief of Bank of America. As the head of litigation at Debevoise & Plimpton, she also represented JPMorgan Chase and the board of Morgan Stanley.

Barbara S. Jones, who retired recently from the federal bench in Manhattan and now practices law at the firm Zuckerman Spaeder, said Ms. White, a close friend, would benefit from both prosecuting and defending executives over her career. “She has been on both sides,” Ms. Jones said. “She will be tough when she has to be, but she’ll be fair.”

At the White House on Thursday, Ms. White spoke only briefly, saying she would work “to protect investors and to ensure the strength, efficiency and the transparency of our capital markets.” Mr. Obama noted that Ms. White, whose 43rd wedding anniversary fell on Thursday, was a childhood fan of “The Hardy Boys,” as he was, adding that she “built a career the Hardy boys could only dream of.” “You don’t want to mess with Mary Jo,” he said.

Peter Baker and Kitty Bennett contributed reporting.