Mathew Martoma, a former portfolio manager at hedge fund SAC Capital Management, has hired a new lawyer to defend him in his insider-trading case.

Martoma has brought in Richard Strassberg at Goodwin Procter to take over his defense, a spokesman for the law firm confirmed yesterday. The former fund manager previously was represented by Charles Stillman, a prominent New York white-collar lawyer with Stillman & Friedman.

In an affidavit filed yesterday in District Court in Manhattan, Strassberg said Martoma sought to replace his lawyers because of Goodwin Procter’s “expertise in the subject matter of this case.”

Strassberg is a former chief of the major crimes unit at the Manhattan US Attorney’s Office.

Martoma is one of several current or former SAC Capital employees charged with insider trading while working at the $15 billion hedge fund run by billionaire Steven A. Cohen.

Martoma has been charged with conspiracy and securities fraud related to trades in Elan Corp. and Wyeth, which now is part of Pfizer.

Authorities said the trades were made based on illegal tips from a doctor and allowed CR Intrinsic Investors, an SAC fund, to earn profits and dodge losses of $276 million in 2008.

Martoma has also been charged in a related civil action by the Securities and Exchange Commission.

Cohen has not been charged with any wrongdoing. SAC has agreed to pay $616 million to settle two civil SEC actions over insider-trading allegations.

One of the settlements, for $602 million, is with CR Intrinsic and stems from the Martoma case.