LOS ANGELES -- Unmarried Californians are doubling up in growing numbers to buy houses in the slumping California market, a real estate trade group reported recently.

The California Association of Realtors said households made up of two or more unmarried individuals accounted for 12 percent of all California home sales last year -- double the level in 1986.

"The surge in the number of nontraditional households buying homes over the past five years was sparked by the state's continuing affordability crisis," said Mack Powell, president of the trade group. "Affordability pressure has forced some unmarried individuals to form nontraditional households to make homeownership possible."

The California housing market, which accounts for as much as a fifth of the national activity, has been stagnant since the summer of 1989, when housing prices peaked. Demand began declining as inflated prices, fueled by sellers' unrealistic expectations, forced many potential buyers out of the market.

The trade group, which tracks sales of existing homes, has forecast a decline of 14 percent in the home resale market this year. New-home sales are expected to fare just as badly.

"We expect to see even greater numbers of nontraditional households in the next several years, mostly because of the affordability crisis and other trends, including the aging population, high divorce rates and lower marriage rates," Powell said.

The survey showed the median age of California home buyers last year was 38 years, up from 35 years in 1989 and 36 years in 1986.

The trade group also said the nontraditional households and unmarried home buyers accounted for about 36 percent of all California home buyers last year, up from 29 percent five years ago.

The association's finance survey also said the median annual income of California home buyers in 1990 was $60,000, unchanged from 1989 but up from $48,000 five years ago.

The only significant gains in home-buying activity in California have come in the inland areas where raw land is significantly cheaper than in the coastal areas near San Francisco and Los Angeles. As a result, the key growth centers are now in places like Riverside, Barstow, Sacramento, Fresno, Modesto, Bakersfield, Redding and Yuba City.

The survey confirmed this move toward less expensive homes, saying that 19 percent of all buyer households had incomes above $100,000 last year, down from 23 percent in 1989. It also showed that about half of all California buyer households earned between $50,000 and $99,999 in 1990, up from 46 percent in 1989 and 37 percent in 1986.

The association also said that about 11 percent of the homes purchased last year were bought in all-cash transactions, more than double the figure in 1985.