The nation's leading auto makers yesterday reported a 22.5 percent gain in sales for mid-April, the sharpest 10-day gain since mid-November 1984, when sales soared 28.8 percent.

The six companies, General Motors Corp., Ford Motor Co., Chrysler Corp., Honda Motor Corp., American Motors Corp. and Volkswagen of America, reported combined sales of 284,490 cars in the United States during the 10-day period of April 11-20, compared with 232,156 units sold in the year ago period.

Nissan Motor Manufacturing Corp. U.S.A., which started production of its Sentra subcompact in the United States last month, said it would not report sales until the end of the month.

Ford Motor led with a 49.6 percent increase as strong sales of its Thunderbird and Mustang models boosted its market share from 21.5 percent a year ago to 26.2 percent.

General Motors had its best mid-April performance since it set a record in 1977, GM spokesman Harold Jackson said. GM's market share was 57.7 percent, up from 55.8 percent in early April and a higher than normal 62 percent last year.

The daily selling rate of 31,610 cars compares with 25,795 for the same period last year, the best mid-April since 1978.