The insurance fund protecting U.S. bank deposits is expected to shrink by $3 billion in 1990, about $1 billion more than expected, the chairman of the Federal Deposit Insurance Corp. said Thursday.

In a separate development, the agency voted to sharply increase the premium it charges banks for protecting deposits.FDIC chief William Seidman said his agency has determined that over the first six months of the year the government's Bank Insurance Fund fell to about $11.4 billion from $13.2 billion - a 14 percent loss.

The FDIC had expected a $2 billion loss for all of 1990, but in an interview Seidman said, "Now we think it'll be $3 billion for the year.

"The losses are larger and there were more failures," Seidman told United Press International.

As for insurance fund losses next year, Seidman said, "It's hard to predict . . . but it appears 1991 will be better than 1990."

The surprising data were released at a meeting of the agency, which insures deposits at the nation's banks up to $100,000. Also during the meeting, FDIC officials voted to increase the insurance premium.

Effective Jan. 1, the premium will increase to 19.5 cents per $100 of deposits. The FDIC had been planning to increase the premium to 15 cents per $100 from the current 12 cents per $100.

Seidman said the 19.5 cent premium "will increase our income and reduce our losses."

He also said the FDIC would consider raising the premium further if the Congress passes legislation granting the agency wider latitude on raising insurance rates.

The sweeping plan is supported by the White House, but Seidman said another increase could cause problems for many ailing institutions.