In spite of flagging sales, the median price for existing single-family houses in California rose to a record $100,661 in July, exceeding the $100,000 level for the first time, according to the California Association of Realtors.

The new median price is eight-tenths of 1 percent above the $99,813 median price for June and was accompanied by a 4.9 percent increase in sales activity in July over June, according to association president John Seymour. However, he added that July volume was 22.1 percent below that of July 1979.

"July activity doesn't show the upsurge in mortgage interest rates in August which could bring renewed dampening in the market," he added. "The impact of this latest interest rate rise will not appear until the September figures are compiled."

The shortage of affordable houses in California is graphically emphasized by the distribution of July sales by price categories, according to Joel Singer, the Realtor association's director of planning, research and economics.

"More than half of all July transactions -- 50.9 percent -- were for houses selling for $100,000 or more," he added.

In Los Angeles, the median price range climbed 3 percent to $109,208 a 20.4 percent increase over the July 1979, price. Sales rose 9.1 percent for the third consecutive month but were 13.5 percent below July 1979 levels.

The Orange County median price range rose to a record $123,205, a 24.7 percent increase over July 1979, Singer said. Sales volume fell 5.7 percent from June, lagging 27.6 percent behind July 1979.

The California median home price index for July was based on reports of 10,973 transactions by 47 realty boards throughout the state, he said. Reports for other areas include:

San Diego: The median price increased 0.4 percent in July to $86,209, and 8.2 percent increase over the July 1979, figure. Sales were 43 percent below July 1979 activity.

San Francisco Bay Area: The July median price was $104,376, but sales volume was 11.5 percent the July 1979, levels.

Riverside/San Bernardino: The median price increased 0.4 percent to $70,820, an increase of 10 percent over July 1979.