A random survey of 150 people in the Washington metropolitan area showed just 13 percent had NOW accounts here. That compares with 64 percent of those interviewed in Massachusetts, where the concept of interest on checking accounts originated a decade ago.

The unscientific study was conducted by four Georgetown University School of Business Administration students in late March at the Cherry Blossom Parade. They found that 19 percent of the respondents had NOW accounts, but many of them were outside this area.

Not surprisingly, NOW account holders proved to be more aware of minimum balance requirements and transaction charges than were people with regular checking accounts. Yet, despite this awareness of costs, two thirds of those surveyed said they chose their financial institution for convenience. Thirteen percent mentioned interest rates and service charges, whereas a scant 5 percent cited service as a reason for selecting a bank or thrift.

The students recommended that financial institutions stress convenience -- location, hours -- more than rates in their advertising. They also suggested Washington area banks and thrifts lower their minimums if they wish to attract more customers. The average minimum balance required by area institutions (based on 24 studied) was $701, compared with a $126 minimum (based on 12 banks) in Massachusetts.

The comparison of rates in a large city with those of an entire state is skewed by the fact that city banks' expenses tend to be higher. Also, median income in this area is considerably higher than in Massachusetts. In 1975, the last year for which statistics are available, median incomes were $19,120 and $15,531 respectively.

According to the American Bankers Association, the Washington area figure is in line with minimums in other large cities that have recently been authorized to offer NOW accounts and with New York, which has had them for several years. A more valid comparison might have been made between metropolitan Washington and Boston.