Black & Decker Co.'s president of just four months is leaving, and earnings in the first quarter of the current fiscal year dropped by 22 percent, the company announced at its annual meeting yesterday.

The announcement of the departure of Ronald H. Fidler reportedly surprised stockholders and analysts at Black & Decker's meeting in Hampstead, Md., near company headquarters in Towson.

There was no explanation for Fidler's move except the terse announcement that he had resigned "to pursue other interests." Fidler had been executive vice president and chief operating officer immediately before becoming president.

Fidler will be replaced as president by Laurence J. Farley, who is executive vice president and chief financial officer. In addition, Farley will take on the title of chief executive officer of the company from Francis P. Lucier, who will remain as chairman.

Lucier said he has served as chief executive officer for eight years and felt it was an appropriate time "to pass along those responsibilities."

The company, which has a large overseas component, has been hit hard by currency fluctuations. Lucier said currency effects accounted for losses of six cents a share.

Overall, Lucier said company earnings for the first quarter of the current fiscal year were $14.4 million compared with $15.1 million last year. Per-share eernings were 34 cents compared with 44 cents.

The company announced sales for the quarter of $299 million, a decrease of 8 percent from $326 million in 1981. Nonetheless, Lucier said the finance committee would recommend payment of the regular quarterly dividend of 13 cents a share.