First Union Corp., the sixth-largest bank in the nation and the third-largest in the Washington area, conceded yesterday that it had slashed its staff too sharply in a cost-cutting move and, as a result, expects its 2000 earnings to fall short of Wall Street's expectations as it scrambles to hire workers.

The Charlotte-based company said it will incur higher costs next year as it hires 2,000 new tellers to lure back customers it has lost since March, when it fired 5,800 workers. The layoffs were part of an effort to reduce expenses after several costly mergers by First Union in recent years, but they ended up alienating many consumers.

"This is in response to customer requests," said First Union spokeswoman Virginia Stone Mackin. "We underestimated the customer's need for 'face time.' "

Analysts said yesterday that First Union told them the bank expects to earn $3.53 to $3.60 a share next year, which would be a 4 percent to 6 percent increase over the $3.40 a share the company expects to earn in 1999.

The company's estimate for next year is well below the earnings of $3.80 a share that Wall Street analysts predicted in November, and even below the $3.65 a share they forecast in recent days.

First Union chief executive Edward E. Crutchfield has already revised earnings estimates for 1999 twice this year, finally settling on $3.40 a share, down from the $4 a share the bank had predicted in the spring and $4.30 it had forecast in January.

"This was a surprise, yes, another surprise," said Marni O'Doherty, bank analyst at Keefe, Bruyette & Woods Inc. "If there were investors out there hoping that the earnings problems at First Union over the course of 1999 could be quickly and easily turned around, well, this suggests it's going to take longer."

Yesterday's earnings estimate was not publicly announced in a news release or during a conference call to analysts, but was given to analysts who phoned the company to find out what its board of directors had decided in a meeting Tuesday, analysts and Mackin said.

First Union's disappointing earnings have diminished Wall Street's confidence in the company and caused the bank's board to shake up management in July. The bank's troubles are sure to fuel continuing speculation in recent months about whether the bank is a takeover target.

Analysts say that despite its problems, the bank has a strong franchise that could be a valuable addition to a financial services company. But they point out that the company has such a large market capitalization--the per-share value of the bank's stock multiplied by its total shares outstanding--that few other banks or financial firms are big enough to take it over.

The company's stock touched a 52-week low yesterday but finished 25 cents above that. It closed at $34.06 1/4, down 87 1/2 cents.