It’s been a tough 48 hours for Wall Street boss Jamie Dimon.

The CEO of JPMorgan Chase is being forced to cough up $156.6 million to settle claims by the Securities and Exchange Commission that the big bank misled pension funds and other investors in selling an investment tied to toxic mortgages.

The SEC claims that in January 2007, JPMorgan structured a $1.1 billion debt security known as Squared, whose underlying mortgage securities were handpicked by hedge fund Magnetar Capital — which was betting against the deal just as the housing market entered a death spiral.

“What JPMorgan failed to tell investors was that a prominent hedge fund that would financially profit from the failure of CDO portfolio assets heavily influenced the CDO portfolio selection,” Robert Khuzami, SEC enforcement director, said yesterday in announcing the settlement.

A day earlier, as federal regulators zero in on conduct by banks before and during the mortgage meltdown, the National Credit Union Administration leveled an $800 million lawsuit against JPMorgan and a second bank charging them with misrepresenting the risks of certain mortgage securities.

JPMorgan’s SEC settlement comes roughly 11 months after Goldman Sachs agreed to a $550 million fine for similar conduct around a separate mortgage-backed investment.

The SEC fell short of charging JPMorgan with “intentional” or “reckless” misconduct since the bank retained an 85 percent stake in the Squared CDO deal and took a roughly $900 million loss in its fixed-income business in 2008, sources say.

“The SEC has not charged the firm with intentional or reckless misconduct,” said a JPMorgan spokesman who noted that the firm did not admit or deny any wrongdoing.

In a separate complaint linked to the Squared deal, the SEC is charging former CDO manager at GSC Edward Steffelin with negligence for marketing materials touting the credibility of his management firm without disclosing Magnetar’s role in selecting Squared’s composition.

Steffelin’s lawyer Alex Lipman at Nixon Peabody, said that the responsibility of disclosing Magnetar’s role wasn’t his client’s.