Although General Motors Corp. sales dropped in early October because of a mid-September strike by the United Auto Workers, combined industry sales rose 4 percent on a daily rate basis, the firms said yesterday.

The six U.S. companies -- GM, Ford Motor Co., Chrysler Corp., American Motors Corp., Volkswagen of America and American Honda -- reported sales of 224,792 autos in the Oct. 1-10 period, compared with 191,965 last year.

There were nine selling days in the period this year and eight last year, which accounts for the disparity in some figures.

The auto makers sold 24,976 cars per day during the period, compared with 23,996 last year. The annual selling rate was 7.4 million, compared with 6.9 million in 1983.

So far this year, the companies have sold 6,325,388 autos, up 22 percent from 5,164,797 last year.

GM reported a 12.7 percent daily rate decline in the period, selling 125,121 cars vs. 127,428 last year. GM sales so far this year are up 19 percent.

The union staged week-long strikes at 17 GM sites in September when it failed to reach agreement by the Sept. 14 deadline. Production of GM's most profitable and popular models was cut severely, leading to shortages of those cars by dealers.

Ford appeared to profit from the GM shortages, reporting a 47 percent increase in sales on a daily basis. Chrysler also appeared to benefit from GM's decline, reporting sales of 27,574 autos, up 21.9 percent on a daily rate basis from 20,114 last year.

Among the smaller companies, AMC reported sales of 3,650 cars, the same as last year, but suffered a 12 percent decline because of the different number of selling days in the period.