A couple of banks lower prime to 11%

Morgan Guaranty Trust Company, the fifth-largest bank in the nation, lowered the prime lending rate it charges its most creditworthy corporate customers to 11 percent Monday, from 11 1/2 percent. Manufacturers Bank of Los Angeles followed the move.

Citibank, Bank of America, Chase Manhattan, and a few other banks have lowered their prime rate to 11 1/4 percent over the past two weeks because of lagging loan demand and an apparent easing of credit by the Federal Reserve.