The average sales price of single-family homes in the District's 55 neighborhoods increased by a record-setting 30 percent during the past 12 months, and one out of 10 homes sold in the city thus far in 1979 has gone for more than $200,000. One of every three D.C. houses sold in the first three months of 1979 cost more than $100,000.

New real estate sales data assembled by D.C. senior residential assessor George B. Altoft reveal that from April 1978 to April of this year, the number of neighborhoods with average home prices of $200,000 or more jumped from one (Massachusetts Heights) to 11 (Georgetown, Spring Valley, Massachusetts Avenue Heights, Forest Hills, Kalorama, Foggy Bottom, Cleveland Park, Berkley, Kent, Observatory Circle and Woodley). Another 16 neighborhoods registered average sales prices of between $100,000 and $200,000, with two more (Mt. Pleasant and 16th Street Heights) only fractionally below that category with average prices of $95,000).

The overall average sales price of single-family homes sold in D.C. rose from $66,000 in the first quarter of 1978 to $86,000 in the first quarter of 1979.

The neighborhood-by-neighborhood price changes in the District's housing stock over the past year "are unprecedented," according to Altoft. "We've just never seen that sort of extraordinarily rapid movement" over so many neighborhoods in so short a period.

City-wide price jumps in the 12 to 15 percent range have been more typical of the inflationary 1970s, but the past 12 months took D.C. off the charts. Although some southern California cities like San Diego have registered huge run-ups in prices of this magnitude or higher in the past two years, no major eastern or mid western city has experienced a boom like D.C.'s.

The price rises are particularly dramatic-though statistically less reliable-in selected sample neighborhoods of the District. The average sales price of homes in Cleveland Park, for example, jumped 66 percent, from $129,400 in the first quarter of 1978 to $215,640 in the first quarter of 1979. These averages are based, however, on just sales during the three-month period of 1978 and eight in the comparable period this year-too small a sample to derive really meaningful conclusions in percentage terms.

In a much larger and more accurate statistical sample, Mt. Plesasnt registered a 40 percent sales price jump between the first three months of 1978 and the same period of 1979. The average price of the 42 homes sold in the first quarter of 1978 was $68,000; the average of the 22 sold this year was $95,140. Mt. Pleasant, known for years as a moderate-priced, in-town neighborhood, had an average sale price of $46,000 in the first quarter of 1976, $54,000 in 1977. The price gains in well-located "back to the city" areas like this "have been nothing short of unbelievable," in Altoft's words.

The city assessment office's statistics indicate that the average sales price of newly constructed single-family homes throughout the District during the first three months of 1979 was $109,360. These ranged as high as $260,000 in Northwest to $43,500 in a Northeast neighborhood.

Altoft, who compiles his data from city tax recordations following realty sale closings, said newly built homes in D.C. are falling into a pattern of "either being for the families who can afford a smaller house in the $50,000s to low $60,000s, or in the luxury, high income being sold or built in the so-called mid ranges of $65,000 to $95,000. The city appears to be telling that segment of the home buying market to look elsewhere."

Data on condominium sales, collected by the city for the first time during the past three months, show an average sales price of $67,720 on 426 transactions. Altoft has no comparable price statistics on these units, but real estate investment specialists say average D.C. condo price gains probably have been slightly less in percentage terms than the massive increase experienced by detached conventional homes. Altoft's quarterly data confirm, nonetheless, that condominiums now account for a substantial chunk of all D.C. residential sales. Roughly 27 percent, or 426 of the 1,568 residential properties sold between January and April were condo apartments or town-houses. Individual condo unit prices ranged as high as $350,000 and as low as the mid-$30,000s.

D.C. Neighborhoods With First-Quarter 1979

Average Prices Between $100,000 and $200,000

Burleith ($135,500), Foxhall ($133,250), Glover Park ($121,100) Palisades ($145,990), Wesley Heights ($187,500), American University Park ($128,100), Chevy Chase ($130,890), Garfield ($180,000), North Cleveland Park ($143,410), Cononial Village ($173,265), Crestwood ($146,350), Capitol Hill ($126,425), Central-Downtown ($173,800), Old City-Far Capitol Hill ($101,175), New Southwest ($128,500), Shepherd Park ($112,630).

D.C. Neighborhoods With First-Quarter 1979

Average Home Sales Price Between $50,000-$100,000

Mt. Pleasant ($95,870), 16th Street Heights ($95,753), Brightwood ($67,775), Chillum ($63,890), Columbia Heights ($51,100), Brookland ($51,615), Ledroit Park ($54,330), Michigan Park ($66,835), Riggs Park ($55,255)8 Hillcrest ($62,900).

D.C. Neighborhoods With First-Quarter 1979

Average Homes Sales Prices Under $50,000

Takoma Park ($49,985), Petworth ($46,785), Brentwood ($43,855), Eckington ($46,335), Trinidad ($40,550), Woodridge ($49,685) Deanwood ($36,330), Fort Dupont Park ($44,635), Lily Ponds ($34,310), Marshall Heights ($35,815), Anacostia ($42,720), Barry Farms ($49,100), Randle Heights ($40,890), Congress Heights ($45,000).