New York Community Bank, the midsize lender under pressure over its real estate loans and internal management, announced an overhaul on Wednesday that included more than $1 billion in emergency cash, the addition of former Treasury Secretary Steven Mnuchin to its board and the appointment of its third chief executive in a month.

The deal was an attempt to shore up a bank that has lurched from shock to shock this year, and attracted the attention of regulators in Washington eager to avoid another banking crisis close to the one-year anniversary of the collapse of Silicon Valley Bank.

The investment of more than $1 billion includes cash from Mr. Mnuchin’s private equity firm, Liberty Strategic Capital, and Kenneth Griffin’s Citadel Securities, among others.

The bank’s new chief executive, Joseph Otting, worked closely with Mr. Mnuchin in the past. He ran OneWest Bank, then owned by Mr. Mnuchin, for five years. He also oversaw the Office of the Comptroller of the Currency, one of the banking industry’s primary regulators, during the Trump administration.

Mr. Otting was a controversial figure in government, feuding with other regulators and angering critics who said his proposals would have defanged rules requiring banks to invest in poor communities and lend to low-income individuals.

The troubles at New York Community Bank began when it posted a $240 million loss in its most recent earnings report in January, mostly tied to apartment and office building investments, surprising analysts and investors and causing the stock to tank swiftly.

Just last week, it replaced its chief executive after disclosing billions of dollars in additional write-downs dating back to 2008, and said it would investigate whether years’ worth of earlier financial disclosures had been accurate. Several credit ratings firms also downgraded the bank.

The Long Island-based lender, which operates more than 400 branches including Flagstar Bank, grew quickly over the past year after acquiring a large chunk of the assets of Signature Bank, another bank that collapsed during last March’s banking crisis.

Thomas R. Cangemi, who led NYCB’s purchase of Signature assets as chief executive before stepping down last month, publicly blamed the pressures of becoming so large so quickly for its recent travails. He said it was forced to comply with regulations that it would not have been subject to as a smaller bank.

Mr. Mnuchin, a Trump administration official, said in a statement that while he was “mindful of the bank’s credit risk profile,” he believed that NYCB had “a strong foundation for future growth.”

It remains to be seen if the moves will work. The bank’s shares plummeted earlier Wednesday when The Wall Street Journal reported that it was seeking to raise capital. The New York Stock Exchange subsequently halted trading in the shares, but when trading resumed after the bank’s public announcement of the overhaul, NYCB shares soared and then fell to flat for the day.

They remain down nearly 70 percent this year.

NYCB had $83 billion in deposits and more than $100 billion in overall assets as of last month. Flagstar is one of the nation’s larger mortgage servicers, tying the bank’s fate relatively closely to that of the housing market.