NEW YORK » When a major bank’s credit rating is cut, it deals a psychological blow — to customers, the public and financial markets.

So Thursday’s downgrading of 15 of the world’s largest banks is almost sure to cause wide concern. Most deposits are perfectly safe, but the downgrades could hurt people in more subtle ways: Banks may jack up fees and might be reluctant to lend, which could affect mortgages, credit cards and even the job market.

"It is normal that the first thing that people worry about is whether their money is safe," said Jim Nadler, chief operating officer at Kroll Bond Ratings Agency. "But the real costs may be hidden."

Bank deposits up to $250,000 are guaranteed by the Federal Deposit Insurance Corporation.

But the downgrades come at a tenuous time for banks. An avalanche of new regulations adopted after the financial crisis has wiped out many of the fees they charged on credit cards and checking accounts. Banks are also barred from making lucrative bets in the stock and bond markets, eliminating billions of dollars in trading income.

So banks are now squeezing income from any place they can. Basic services that were once free now cost money. Checking accounts can cost $8, a bank statement $3, canceling a check $2. The list goes on.

In light of the lower ratings, existing fees might climb further and new ones could appear.

"Banks are going to figure out a way to extract revenue from the customer in any way, shape or form," said Stanley J.G. Crouch, chief investment officer at money manager Aegis Capital.

The top ratings agencies — Moody’s, Standard & Poor’s and Fitch — hold immense sway over how much every company and state or local government pays to borrow money. They assign ratings on a scale that determines the ability of those entities to pay down their debt.

The downgrades could eventually increase the banks’ cost of borrowing in financial markets because investors will demand more interest when they lend the banks money. With interest rates hovering near record lows, most analysts say the cost of borrowing won’t be affected immediately. However, if the ratings remain at these levels and interest rates rise, banks will pay dearly.

For now, investors aren’t worried. The stocks of downgraded banks rose Friday. Bank of America gained 1.5 percent, while JPMorgan Chase and Morgan Stanley each rose 1.3 percent.

The downgrades also suck capital out of banks. That’s because all the large banks sell insurance to investors to protect them from losses on bonds in case of a default.

The downgrades will force banks to set aside billions of dollars in additional reserves because the debt they are insuring has suddenly become riskier. Each notch in the ratings scale triggers automatic requirements for additional money a bank must set aside in reserves.

Because of those requirements, the downgrades will funnel money into reserves and reduce the amount of capital that banks have to lend.

Americans will experience it when they go to their banks for home mortgages, car loans and credit cards.

Already those lending markets are extremely tight.

Since the financial crisis and the bursting of the real estate bubble, banks have become very choosy about lending. During the real estate boom, banks gave out mortgages without checking if people held jobs, whether their income was real and without taking any upfront money.

Today, millions of first-time home buyers are finding it hard to qualify for home loans unless they have stellar credit, a steady employment history and at least 20 percent of the home loan in cash. Experts say the downgrades will make it difficult for banks to provide much relief to less-qualified home buyers.