Deposits in commercial banks in the Washington metropolitan area rose 6.21 percent in the past year to $14.702 billion on Sept. 30, compared with $13.843 billion a year ago, a Washington Post survey has found. Washington, Maryland and District of Columbia banks all posted increases in total deposits over the same date a year ago, though some areas reported a decrease in deposits since the previous quarter.

Regionally, District banks posted the largest annual increase, logging a 9.52 percent advance in deposits to a total of $7.2 billion, up from total deposits of $6.6 billion in September 1980. District deposits showed a slight decline during the quarter ending Sept. 30, slipping 2.87 percent from the total reported on June 30.

Virginia banks registered a more moderate gain, with deposits registering a 3.72 percent increase to $3.54 billion in September, compared with $3.41 billion a year ago. Deposits during the quarter fell 0.82 percent.

In Maryland, banks posted the smallest yearly increase in deposits, up 2.70 percent over the 1980 figure of $3.81 billion to $3.92 billion. Deposits rose during the quarter to $3.57 billion from $3.54 billion, an 0.82 percent increase.