Condominium sales nearly doubled in the District last year, in the face of high interest rates and tight money, and the boom has continued into the new year -- even as house sales have dropped off, the city's real estate assessment office reports.

Senior residential assessor George B. Altoft said that 3,600 converted and new condominiums were sold in the District during 1979, a 96 percent jump over the 1,820 sold in 1978.

The pace accelerated further in 1980, Altoft found, with sales of 536 condo units recorded during the first 60 days. February's 218 recorded 10 days of March saw 93 unit sales, compared with 61 during the comparable period in 1979.

The "amazing D.C. condo market," in Altoft's words, is running counter to the slowdown in sales of detached houses that began last year. Altoft's data, drawn from property transfer records, shows a decline of about 16 percent in house sales thus far in 1980 when compared with the same period last year.

The much lower price of condominiums has clearly been behind the boom in sales here. Condos sold for an average of $71,000 in the city last year, about $24,000 behind the average for single-family houses. Average prices within individual condominium buildings, however, rose 20 percent or more in many instances last year.

Prices at The Analoston at 1718 Corcoran St. NW, for example, rose by more than 60 percent in 1979, when three apartments old for an average of $78,200.

Other condominium projects where more than five units were sold last year and where average prices increased by 20 percent or more included: