Deposits at commercial banks in the Washington metropolitan area rose 6.51 percent in the past 12 months to a record $13.843 billion on September 30 compared with $12.996 billion recorded a year earlier, according to a Washington Post survey. All three areas surveyed showed increases in total net deposits, and only a handful of individual banks recorded decreases from Sept. 30, 1979.

On a regional basis, Maryland depositors posted the largest annual increase, showing a 9.18 percent advance in savings, up from total net deposits of more than $3.499 billion in Sept. 1979 to just over $3.817 billion this year. Maryland deposits showed an increase of 4.36 percent during the quarter ended Sept. 30, up more than $159.64 million from the $3.658 billion total compiled on June 30.

District banks and their branches registered more moderate growth, with total deposits climbing 7.76 percent to more than $6.607 billion in September 1980 compared with more than $6.131 billion a year ago. Net increase for the quarter was 1.02 percent.

In Virginia, deposits rose to more than $3.418 billion, up just 0.9 percent over last year's figure of $3.366 billion. The quarterly increase, from $3.320 billion recorded June 30, was 2.94 percent.