Only one family in six in the Baltimore area can afford an average-priced home, a sharp contrast with nine years ago when half of the families in that area could afford such homes, according to statistics released yesterday.

The precipitous drop in the number of persons with the ability to buy was caused by factors that include higher prices and higher mortgage rates, according to a Regional Planning Council report that was based on average sales figures from the Federal Home Loan Bank Board.

The study, which included Baltimore City and Anne Arundel, Baltimore, Carroll, Howard and Harford counties, showed an average home sales price in 1981 of $82,500 and an average mortgage interest rate of 14.14 percent.

In 1973 the average sales price for the five county region was $35,200 and the average mortgage interest rate was 7.76 percent.

One of the reasons for the decline in housing affordability, the council said, was housing demand, which it said grew at a "staggering rate" in the Baltimore metropolitan area between 1970 to 1980, increasing by 133,000 households.

The greatest leap in home prices occurred during 1980 and 1981, when the cost of buying a house rose nearly 18 percent, according to the study.