Retail sales rose 1.6 percent in November to a seasonally adjusted $81.8 billion, the sixth consecutive monthly increase, the Commerce Department reported yesterday.

Sales at durable goods stores, including automobile dealers, increased 2.3 percent from October, to $26.1 billion. Sales of nondurable goods rose 1.3 percent to $55.8 billion.

While sales of autos and parts rose 1.7 percent in November, to $14.5 billion, they remained below the $14.7 billion level of September and were slightly below their year-earlier level as well, the department said.

Despite the month-to-month gains in new-car sales, information about the pace of buying during the month reported by the industry indicates sales tailed off as the month progressed.

Separately, the department's Bureau of Economic Analysis reported U.S.

nonfarm businesses plan to increase capital spending 5.3 percent in the first quarter of 1981 and 4.3 percent in the second quarter.

According to a survey of investment intentions conducted in October and November, such spending for new plants and equipment will reach a seasonally adjusted annual rate of $317.2 billion in the first half of 1981. That would be a 7.3 percent increase from the second half of this year.

However, capital goods prices have been rising at a 9 1/2 percent rate so far this year. If inflation continues at that rate, BEA said, the spending increases planned for the first half of 1981 would mean about a 2 1/2 percent increase in real terms, that is, after adjustment for inflation.

Actual spending by these businesses rose 0.5 percent in the third quarter of this year, while the survey indicates it will fall by about the same amount this quarter. The latest estimate for all of 1980 is $294.3 billion, up 8.8 percent -- less than the rate of inflation -- from 1979.