Chase Manhattan, the nation's third-largest bank, raised the prime lending rate it charges its most creditworthy corporate customers to 18 1/2 percent from 17 3/4 percent. Other major banks promptly did the same. The step was taken despite a $1.9 billion drop in the nation's money supply. Analysts said Chase made the move presumably because of rising costs it must pay for funds and concern tht surging rates will cause the economy to slump again. The 8 1/2 -percent level is one many economists predicted would be a peak, but a growing number now believe the rate could hit the record 20 percent level it reached last spring.