New York ? The big banks are showing they can still make money, even as Main Street struggles — though not from lending, refinancing homes or other bread-and-butter business.

Instead, they’re doing what Wall Street does best — betting big on stocks, bonds, commodities and other assets.

Citigroup, the shakiest of the major banks during the financial crisis, reported Thursday it eked out a quarterly profit from trading, despite suffering more losses on consumer loans. Trading also drove big profits at Goldman Sachs and JPMorgan Chase.

That some banks are making money now is a sign of remarkable recovery from the crisis a year ago. But the lopsided business model raises questions about what happens if trading profits fall off and banks are left to rely on more traditional operations.

After all, the economy is still struggling to recover, unemployment is approaching 10 percent and Americans are saving money and trying to pay down debt, not taking on more.

“The good news is that banks are in better shape. The bad news is that they’re not making loans to consumers and businesses,” said market analyst Edward Yardeni. “That could come back to bite them because these trading gains will only last so long.”

Mindful of the problems banks still face, investors reacted cautiously a day after the Dow Jones industrials powered back above 10,000 for the first time in a year. Stocks zigzagged for most of Thursday before ending modestly higher.

For now, trading is pretty much the only way banks can make money. And it’s more lucrative because there are fewer competitors, interest rates are near zero and government subsidies have allowed banks to borrow cheaply and invest in assets that offer the highest returns.

Goldman Sachs Group Inc. has benefited more than most. Famed for its trading prowess, the New York investment bank said Thursday that third-quarter earnings swelled to $3.03 billion, more than triple what it made a year ago.

As in past quarters, Goldman leaned heavily on its trading operation — buying and selling stocks, bonds, foreign currencies and commodities like oil and gold — to make money.

“They’ve been on the mark on the trading side,” said Stephen Hagenbuckle, a principal at private equity fund TerraCap Partners.