NEW YORK (AP) _ Stocks plummeted in the busiest trading ever on the New York Stock Exchange Friday as the Dow Jones average of 30 industrial fell more than 100 points for the first time.

The Dow average fell 108.36 points to 2,246.73. Volume was a record 338.48 million shares.

''It's extremely emotional. People are dumping stocks with reckless abandon,'' said Newton Zinder, a veteran market analyst at E.F. Hutton & Co. ''As trite as it may sound, the market is going down because it's going down.''

The triple-digit decline was less impressive in percentage terms. Dow Jones & Co. said the drop was the 76th largest in percentage terms in the history of its average, which dates back to 1896.

Friday marked the third day of heavy selling. The Dow average lost 95.46 points on Wednesday, the previous record point drop, and then tumbled 57.61 points on Thursday.

For the week, the Dow's drop was 9.5 percent.

Plaguing the market have been worries over the nation's persistent trade deficit and fears that a falling dollar could mean higher inflation and higher interest rates.

The latest sell-off seemed to be triggered by Wednesday's report that the nation's merchandise trade deficit was a bigger-than-expected $15.7 billion in August.

The Reagan administration, seeking to calm the markets, issued a statement Thursday declaring that it expected interest rates to turn downward soon.

Analysts were reluctant to predict that the five-year bull market was over, noting that the Dow's drop left it well above its value at the beginning of the year.