INDIANAPOLIS (AP) _ Strong sales of the antidepressant Prozac keyed a 19 percent rise in first-quarter earnings by Eli Lilly and Co., the pharmaceutical maker reported Monday.

Lilly said it earned $393.2 million, or $1.36 per share, during the first three months of the year, compared with $330.7 million, or $1.12 per share, for the same period in 1994. Sales rose 31 percent to $1.71 billion from 1.31 billion.

Of the sales growth, 29 percent was due to higher volume. Favorable foreign exchange rates added 3 percent, offset by a 1 percent decline in prices, the company said.

Domestic sales grew 36 percent and overseas sales were up 28 percent.

Prozac, which accounts for more than a quarter of Lilly's total revenue, saw a sales gain of 36 percent to $456.7 million. Lilly said it expected Prozac sales to continue growing through the end of 1995 but at a lower rate.

Prozac's price was increased 2 percent on March 22, according to MediSpan, a drug-price tracking service.

Lilly said strong sales of the drugs Axid, for ulcers, Ceclor, an antibiotic, and Humulin, an insulin replacement, also contributed greatly to the overall sales growth. Revenues from PCS Health Systems, the prescription benefits manager Lilly bought last year, also contributed to the 1st quarter revenue rise, the company said.

``Our strong operational performance for the first quarter is a direct result of our ability to develop and then, very importantly, implement a strategy aimed toward a leadership position in the global marketplace,'' Lilly Chairman Randall L. Tobias said.

The company said the addition of PCS and the global marketing effort led to a 45 percent rise in its marketing and administrative costs during the quarter. It also said research and development costs rose 34 percent, partly because of a large number of compounds entered the latter stages of experiments on humans.

Lilly's results exceeded Wall Street analysts' expectations. Its shares, which have been rising fairly steadily for the past year, gained $1.12 1/2 to $78.87 1/2, a 52-week high.