WASHINGTON — The man who nearly 40 years ago co-founded what is now the nation’s largest mortgage lender is being scrutinized by federal securities regulators as they examine his sales of the struggling company’s stock.

The Securities and Exchange Commission’s informal inquiry into the chief executive of Countrywide Financial Corp., Angelo Mozilo, has been under way for a while, a person familiar with the matter said yesterday. The person spoke on condition of anonymity because the probe has not been made public.

Mr. Mozilo, who moved the company in 1969 from New York to the housing hotbed of suburban Los Angeles, has guided Countrywide through numerous boom-and-bust housing cycles. Now, Calabasas, Calif.-based Countrywide is cutting thousands of jobs amid the nation’s mortgage crisis, and its shares have fallen more than 50% since January.

Mr. Mozilo sold some $130 million in Countrywide stock in the first half of the year through a prearranged 10b5-1 trading plan. The plans, popular among corporate executives, allow a company insider to set up a program in advance for such transactions and proceed with them even if he or she comes into possession of significant nonpublic information.

The SEC has been casting a wide net in its scrutiny of Wall Street banks, investors, credit-rating agencies, and others and the role they played in the subprime mortgage crisis.

The state treasurer of North Carolina, Richard Moore, last week asked the agency to investigate Mr. Mozilo’s stock sales. Mr. Moore raised questions about changes made to Mr. Mozilo’s plan in the months before the company’s stock plunged, allowing Mr. Mozilo to significantly increase his sales of Countrywide shares.

Mr. Mozilo has sold company shares through prior arrangements since 2004; the pace of his sales began to quicken last October when he put a new plan into effect. Mr. Mozilo, who is 68, said recently that he did so to reduce his stake in Countrywide and diversify his personal investments in an orderly fashion in advance of his retirement, slated for December 2009.

Mr. Moore, the trustee of a pension fund that holds about 500,000 shares of Countrywide stock worth some $8.6 million, said in a letter to SEC Chairman Christopher Cox that he was “shocked” to learn Mr. Mozilo “apparently manipulated his trading plans to cash in” as the crisis involving high-risk mortgages was heating up.

“As one of many investors who have felt the painful losses in Countrywide stock, I am outraged at his manipulation of the system and this abuse of shareholders,” Mr. Moore, a Democrat who is running for governor, wrote. “The timing of these sales and the changes to the trading plans raise serious questions about whether this is mere coincidence.”

Word of the SEC’s inquiry “is good news for investors and sends a clear message that the questions raised are serious,” Mr. Moore said in an e-mailed statement yesterday.

Countrywide representatives didn’t respond to a request for comment.