Revenue is back.

Hard-hit by new regulations and a sluggish economy, banks have struggled to revive top-line performance since the financial crisis, even as profits improved. But two of the nation’s largest lenders, JPMorgan Chase and Wells Fargo, reported strong revenue growth Friday, a surprise that could bode well for the rest of the industry and the broader economy.

“For the expansion to be sustained, it is important that the banking sector be healthy and willing to extend credit,” said Dean Maki, chief U.S. economist at Barclays. “We’re seeing the banking sector turn more expansionary.”

Indeed, Federal Reserve data show that total bank lending grew at an annualized rate of 5.4 percent in the first two months of 2012, compared with a rate of 4.2 percent in the second half of 2011.

Still, bank stocks were down sharply Friday in part on concerns that the first-quarter gains may be fleeting and over the European debt crisis.

At JPMorgan, the country’s biggest bank by assets, revenue rose 6 percent, to $26.71 billion, compared with the quarter a year ago.

It was partly because of strong demand for mortgages, business loans, as well as healthy trading volumes on Wall Street. That was $2 billion more than analysts had expected.

For Wells Fargo, which recently supplanted Bank of America as the nation’s leading mortgage lender, home loans were also a source of strong growth, as was lending to corporations. Revenue at Wells Fargo rose 6 percent, to $21.64 billion, the highest level in more than two years. Until now, the bank’s revenue had steadily declined for several quarters. In the first quarter of last year, for instance, the bank’s revenue dipped 5 percent.

“There is nothing not to like here,” said Christopher Kotowski, an analyst with Oppenheimer.

Unlike the first quarter of 2011, earnings growth came largely from underlying operating strength, while one-time gains from the release of reserves for credit losses actually dropped.

Banks in recent quarters have bolstered profits by reclaiming billions of dollars they had reserved for expected losses from unpaid loans to businesses and consumers. JPMorgan Chase released $1.7 billion from reserves compared with $2.6 billion a year ago, while these gains totaled $400 million at Wells Fargo compared with $1 billion a year ago.

“Core earnings were stronger than we were looking for,” Kotowski said. “Most of the loan portfolio was growing and credit quality was well-behaved.”

Despite the better-than-expected results, bank stocks suffered profit-taking Friday after a strong run recently. The market also declined after news that the Chinese economy was slowing and Spanish borrowing costs were spiking. Shares of JPMorgan Chase dropped 3.6 percent, to $43.21, while Wells was down 3.5 percent, to $32.84.

Some analysts question whether the revenue recovery is sustainable. The revenue gains, some say, could be fleeting because banks still face a sluggish economic recovery and a new round of federal regulations that restrict the fees they can charge consumers. And the improvements stem in part from the booming refinancing business, which will most likely slow once interest rates climb.

“I think people will be wary of reading too much into it,” said Jim Sinegal, an analyst at Morningstar. “It would be more encouraging if it was a sustainable recovery in the mortgage business.”