Black & Decker Manufacturing Co. said yesterday it will borrow $55 million from a consortium headed by a British bank.

The medium-term loan, worth about $130 million at recent exchange rates, was negotiated with Morgan Grenfell, a London bank, and carriers an interest rate slightly higher than the company might have to pay an Amererican bank. However, a tax credit and the loan's value as a hedge against fluctuations in foreign currency are expected to offset the difference in rates, a Black & Decker spokesman said.

The loan rate is tied to the London inter-bank borrowing rate which is generally slightly higher than the prime rate in the United States that provides the base for most corporate loans. Black & Decker will repay the loan on a semi-annual schedule beginning in January 1985 and ending in 1987.

What Black & Decker is doing is what a number of other U.S. corporations have done -- borrow foreign currency in order to have both liabilities and assets in the same currency as a hedge against changing currency values. In other words, if the value of the company's assets which are tied to the pound goes down, so does the libility the company has incured in the same currency.

At the end of 1979, non-bank U.S. borrowers had approimately $16.9 billion in liabilities to foreigners, according to figures published by the Federal Reserve Board. Included in that figure was about $3 billion in borrowings in foreign currencies. Most of the liabilities are with lenders in the United Kingdom, Japan, and Middle East oil exporting countries.

Black & Decker has substantial operations in the United Kingdom -- approximately 15 to 20 percent of its worldwide business is there, said William Hammer. About 60 percent of the company's total business volume is outside of the U.S. and that percentage is growing, he said.

The loan represents the first time the company has gone to a non-U.S. lender for longterm financing, he said. Approximately 14 depositing banks, including other banks in the United Kingdom, banks in the U.S. and in other parts of Europe, are participants in the loan along with Morgan-Grenfell.