First Union Corp., the sixth-largest bank in the nation and the third largest in the Washington area, announced a management shake-up yesterday prompted by disappointing earnings and lack of confidence on Wall Street.

The Charlotte-based banking giant said that President John R. Georgius, 54, will retire at the end of the year and be replaced by G. Kennedy Thompson, 48. Georgius, who has worked at First Union for 24 years, has been in charge of the bank's troubled effort to streamline its branch operations by encouraging customers to use the telephone, automated teller machines and computers rather than live tellers for routine banking questions and transactions.

The approach has alienated many customers, bank industry analysts say, especially those at First Union's newly acquired bank, CoreStates Financial Corp. of Philadelphia, for which it paid $20 billion last year. First Union has said that it has lost 19 percent of CoreStates' retail customers over the past year, about twice what analysts say is typical when a bank is acquired.

The bank stands by the approach but concedes that it may have been too "aggressive" in trying to implement it while also integrating an acquisition, said company spokeswoman Laurie Hedrick. The purchase of CoreStates was part of a three-year buying program that First Union chairman and chief executive Edward E. Crutchfield has told analysts is now over.

Thompson is in charge of First Union's investment banking, which has been a bright spot in an otherwise disappointing earnings picture.

The bank, which surprised Wall Street investors twice earlier this year by cutting earnings estimates, now says it expects to earn $3.40 to $3.50 a share for 1999, down from the $4 the company had predicted in January.

In an emergency meeting yesterday, First Union's board of directors voted to put Thompson on the board immediately and to make him president as soon as Georgius retires. Industry analysts and executives believe that Georgius was pressured to step down. First Union officials denied that yesterday.

"This is a positive step, but it doesn't mean they are out of the woods," said Peter Kuper, an analyst at Keefe, Bruyette & Woods Inc. in New York. He said the action signifies that "the board is trying to show Wall Street that they mean business" and that Georgius has "gracefully agreed to step aside to allow some other successful managers to step up to the plate."

But he and other analysts cautioned that changing top management doesn't necessarily fix the core problems, including retrieving lost customers.

Sandy Flannigan, a bank analyst at Merrill Lynch & Co., described the change as "the start of the company putting into place a younger team" and said, "Any time you have a series of missteps you go back and think, 'Do we need to make some changes?' "

Some industry executives and analysts speculated that if the company's performance does not improve substantially, Crutchfield also might be pushed out.

Flannigan disagreed. "Crutchfield is as energized as I've seen him in year and focused on the day-to-day operations of the company," she said. "Ed's built a great company. There's been some missteps along the way, but I don't think anyone can deny the formidable franchise that he's built."

First Union's stock closed yesterday at $48, up $1.12 1/2 in trading on the New York Stock Exchange.