Personal income grew by only 0.2 percent in December, the smallest monthly gain since April 1980, the Commerce Department said yesterday.

In a separate release, the department reported a rise in housing starts from their November level of 863,000 to a still-depressed annual rate of 978,000 in December. In 1981 as a whole, only 1.086 million units were started, the department estimated. This is the lowest rate for any year since 1946 and 15.9 percent below the 1980 rate.

The December rise in personal income was almost certainly too small to offset inflation, and it added to the evidence that the economy slipped deeper into recession last month. Private wages and salaries fell by just under 0.1 percent in the month to an annual rate of $1.525 trillion, the Commerce Department said. They had risen by 0.6 percent in the previous month.

Factory payrolls also fell last month, by 0.7 percent, to an adjusted annual rate of $388.7 billion after falling 0.6 percent in November.

The Commerce Department's chief economist, Robert Ortner, said it was not surprising that total income grew so slowly last month, because unemployment rose sharply to 8.9 percent as firms laid off workers. However, he repeated the administration's view that the recession will end soon. The economy, "like the flowers, will begin to bloom again in the spring," Ortner commented.

Despite the weak growth in incomes, personal spending rose 0.7 percent last month to an adjusted annual rate of $1.924 trillion, the Commerce Department report showed. Savings as a proportion of income slipped to 5 1/2 percent last month from 6 percent in November and 6.3 percent in October, when there was a boost to incomes from the president's tax cut.

For 1981 as a whole, personal incomes climbed by 11.3 percent, up slightly from the 11.1 percent rise between 1979 and 1980. Last year's gain in disposable incomes is estimated at 2.1 percent after allowing for tax and price rises, the Commerce Department said. In 1980 the gain was 0.7 percent. Most of last year's improvement came at the beginning of the year.

Farm incomes fell by 6 percent last year, even more taking account of inflation, the Commerce Department said.

With record-high interest rates in 1981, interest income leaped by 20.4 percent between 1980 and 1981, the Commerce Department reported. High interest rates brought on the present recession, hitting the housing and auto industries first.

Most analysts expect housing to pick up this year from last year's levels, but the industry fears that a renewed rise in interest rates could stifle the recovery. The December starts were up 13.3 percent from November, largely because of a 47 percent increase in the starts of buildings with five or more apartments.