Real estate sales in the Washington area totaled more than $9.6 billion, an increase of 23 percent over 1983, according to figures compiled by Rufus S. Lusk & Son Inc.

The data also showed that Fairfax County continues to be the area's busiest market, accounting for $3.98 billion worth of sales and 27,473 of the nearly 70,000 transactions in the area's four largest jurisdictions.

Of these four jurisdictions -- the District, Prince George's, Montgomery and Fairfax -- all recorded substantial increases in dollar volume over 1983, and all but Prince George's showed more transactions. The number of sales dipped slightly in Prince George's -- 2.5 percent to 12,959 -- but dollar volume there climbed 16.2 percent to $1.3 billion, according to Lusk.

Overall, Washington-area real estate sales topped $7.8 billion in 1983, Lusk reported.

Prince George's continued to distinguish itself as the most affordable area around Washington, with only a single neighborhood, Glenn Dale, showing an average house price above $100,000. On the other hand, the average price of a condominium in the Fort Washington area, $131,711, was one of the highest in any jurisdiction, Lusk said.

Capitol Heights was the least expensive area for houses, with an average of $54,464.

Overall, a single-family home in Prince George's cost $80,754 on the average last year, while condos in the county cost $57,168 on the average.

Lusk is a real estate information and publishing company based here. It tracks real estate transactions in all local jurisdictions and issues publications based on them. The company now has its information on the four largest jurisdictions in computer form, which allows it to make period reports analyzing the markets in those four.

However, its computer analysis capacity does not yet include Alexandria and Arlington, nor does it include more distant counties, such as Prince William and Howard.

Its recent report on Prince George's, the last of its annual roundups in the four big areas, notes that as in the District and Montgomery, mortgages held by sellers are the largest single source of financing. In Prince George's there were 948 first trusts taken back by sellers, totaling $103.7 million.

These notes accounted for 8.8 percent of all first trusts and 9 percent of the first-trust dollar volume.

Among institutional lenders, United Mortgagee was the leader, as it was in 1983, writing 811 loans for a total of $57.9 million. It held an 8.5 percent share of the market.

Second was Standard Federal Savings & Loan, with 759 loans totaling $57.1 million. Guaranty Mortgage was third with 648 loans totaling $43.7 million.

The most expensive property to change hands in Prince George's last year was Iverson Mall, a 25-acre parcel along Branch Avenue that went for $25 million.

The top residential sale was boxer Sugar Ray Leonard's house in the Sunset Valley subdivision of Bowie, bought by Mr. and Mrs. Ervin C. Bender for $425,000. Notably, the sellers took back a $325,000 mortgage in the sale. Indeed, seller take-backs or assumptions figured in four of the top five home sales in the county last year, and in six of the top 10, according to Lusk.

The leading builder in the county was Ryland Homes, with 247 sales totaling $20.2 million and accounting for a 7 percent share of the new-home market, Lusk said. The average Ryland price was $81,822.

In second place was Washington Homes with 226 sales, totaling $15.5 million, for a 6.4 percent market share and a $68,776 average.

The Lusk data shows some contrasts in the jurisdictions' new home markets. For instance, while none of the 10 largest builders in Prince George's average over $100,000, seven of the top 10 in Fairfax did. And while the overall average price of a house in Montgomery was $115,248, only two of that county's 10 busiest builders averaged more than $100,000.

The 10 busiest builders in Fairfax last year had a combined average price of $108,124. The comparable figure for Montgomery was $90,613, and for Prince George's, $69,858. In all three jurisdictions, the builders' average was lower than the overall average -- not a surprising finding in view of the big-volume builders' efforts to price their products to as wide a market as possible.

The number of new homes built in the District was too small to make a meaningful comparison.