NEW YORK (Reuters) - Big U.S. banks revealed more evidence of a slowdown in loan growth in their earnings reports on Thursday, though executives assured there is still healthy demand from borrowers and no reason to worry about the state of the economy.

JPMorgan Chase & Co JPM.N and Citigroup Inc C.N posted higher first-quarter earnings that beat analysts' expectations on large gains in trading revenue. Wells Fargo & Co WFC.N, which relies more on traditional lending and less on markets-related businesses, reported a slight dip in profit due to a slowdown in mortgage banking.

The results underscored concerns expressed recently by analysts and investors that higher interest rates, combined with uncertainty about geopolitical events, could hurt economic growth - and therefore crimp lenders’ bottom lines.

But on conference calls to discuss results, top bank executives dismissed those concerns, citing strong demand from borrowers with impressive credit quality.

“I wouldn’t overreact to the short term in our loan growth with so many things that affect it,” said JPMorgan Chief Executive Jamie Dimon.

The bank’s core loan portfolio averaged $812 billion during the first quarter, up 9 percent on an annualized basis. But that growth rate has ticked down from 12 percent in the previous quarter and 17 percent a year ago. Wells Fargo’s annual loan growth rate of 4 percent has also been slowing over the past year.

Citigroup’s loan book has been skewed by divestitures and its acquisition of a credit-card portfolio. Adjusting for those matters, Citi’s core loan book grew 5 percent in the first quarter, executives said. But management’s outlook for loan growth has nonetheless been tempered.

“There was probably just some modest reduction in our expectation for loan growth ... compared to the earlier guidance, certainly following the first-quarter performance,” Chief Financial Officer John Gerspach said.

Across the banking industry, loans fell slightly during the first three months of the year, according to Federal Reserve data.

John Conlon, chief equity strategist at People’s United Wealth Management, who invests in bank stocks, said he is still concerned about loan growth after seeing the reports and listening to the executives’ comments.

“There’s a great deal of optimism,” Conlon said, “but there’s still uncertainty.”

Wells Fargo's shares were down 2.6 percent at $51.75, while Citigroup's stock was down 0.7 percent at $58.12 and JPMorgan fell 0.6 percent to $84.88. The KBW Nasdaq Bank Index .BKX fell 0.8 percent.

The mortgage business is putting particular pressure on loan growth. The recent uptick in interest rates has crushed a wave of mortgage refinancing that kicked off in 2010, leading to big declines in mortgage banking revenue.

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Other areas of lending have also slowed. For instance, some big corporate borrowers have been opting to issue bonds rather than take out traditional loans, JPMorgan Chief Financial Officer Marianne Lake said.

And, in areas where banks are finding growth, like credit-card lending, they are doling out fat rewards and cutting interest rates to lure customers from one another.

Even so, bank executives sounded optimistic on Thursday about the outlook for lending.

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Higher rates allow banks to earn more money from the loans they make, as well as the idle cash they have invested in low-risk securities like Treasury bonds. JPMorgan expects to add another $400 million to its net interest income in the second quarter. That metric is important because it shows the difference between what banks pay for funds and what they earn from using them.

Additionally, they said, signals that lawmakers and the White House want to spur the economy bode well for loan growth. Citigroup Chief Financial Officer John Gerspach said first-quarter lending reflects some waiting by borrowers for Washington to act.

“We haven’t seen concrete changes yet in policies,” Gerspach said. “When we get tax reform [and] when the administration is successful in implementing some of what they have been talking about - hopefully that will spur the economy on.”