FORT WASHINGTON, Pa. (AP) _ Newly merged pharmaceutical manufacturer Rhone-Poulenc Rorer Inc. reported on Thursday it earned $1 million in 1990, after taking a $289 million charge for restructuring costs.

Prior to its July, 1990 merger with Paris-based Rhone-Poulenc, Rorer Group Inc. reported 1989 earnings of $84.9 million or $2.43 per share. The merged company said its earnings amounted to 2 cents a share.

RPR, based in Fort Washington, Pa., reported profits of $162.8 million for the fourth quarter of 1990 or $2.42 per share, compared to net income of $43.9 million or $1.12 per share for Rorer alone in the fourth quarter of 1989.

The fourth quarter 1990 results were boosted by $78.8 million from sales of assets, the company said. Rorer made gains of $25.9 million in the fourth quarter of 1989 through similar asset sales.

''As can be seen from the fourth-quarter results, we are already seeing the expected benefits of the merger and have achieved our objective of breaking even in 1990,'' said RPR President and Chief Executive Robert Cawthorn.

RPR said fourth-quarter sales grew 18 percent, to $1.1 billion, the company said.

The company said 1990's growth was reduced by unusually high sales in the fourth quarter of 1989 due to a flu epidemic in Europe in 1989, coupled with management's decision not to allow large year-end purchases in anticipation of price increases in the U.S. prescription and German over-the-counter markets.

RPR was created in July with the merger of the former Rorer Group Inc. and the pharmaceutical businesses of Rhone-Poulenc S.A., based in Paris. On May 5, Rhone-Poulenc completed its tender offer for 50.1 percent of the outstanding shares of Rorer.

The 1990 results include 12 months of operations for divisions of the company formerly associated with Rorer and operations of the former Rhone- Poulenc businesses since May 5.