How will former federal prosecutor Mary Jo White perform as the new head of the U.S. Securities and Exchange Commission? Barron’s “D.C. Current” columnist Jim McTague offers some perspective.

Expectations are high that she will get tough on the Street and silence critics who claim that the Obama administration let the big fish responsible for the 2007 credit collapse get away with high crimes and misdemeanors. However, White at times has been as cozy with the Street as she has been tough with it. So it remains to be seen if she will live up to the current hype.

White was U.S. attorney for the Southern District of New York from 1993 to 2002 — one of the most prestigious postings in the Justice Department. The crime fighter helped pack the slippery Mafia godfather John Gotti off to jail after he had beaten three previous prosecutions. White’s team also successfully prosecuted big-time terrorists and a laundry list of Wall Street malefactors. Most memorable for investors was the prosecution of the former Prudential-Bache Securities for misleading 120,000 investors about the riskiness of $1.4 billion in oil and gas limited partnerships from 1983 to 1990. That case resulted in probation and a stiff settlement for the firm rather than a drawn-out court battle — a template later followed by the SEC.

Obama has raised expectations that White will transform the SEC from a bumbling Barney Fife wielding an unloaded six-shooter into a tough, decisive force that protects the public instead of coddling the big financial firms. …

… White has played big-time defense as well as offense. When she left the U.S. attorney’s office and became head of the litigation department at Debevoise & Plimpton in New York, she went to bat against the government for a list of big-name financial-sector clients, most notably Bank of America’s Ken Lewis.

She also has worked in the financial sector, having served as a Nasdaq director from 2002 to 2006. Tom Joyce, the CEO of Knight Capital, was one of her colleagues. His firm last year lost $461.1 million in 30 minutes owing to a computer glitch, pressuring the SEC after years of dithering to crack down on high-speed computerized trading.