BASEL, Switzerland (AP) _ Swiss drug and chemical company Ciba-Geigy AG said today it is buying Rhone-Poulenc Rorer's U.S. and Canadian non-prescription drug lines for $407 million.

The deal combines Rhone's popular antacid Maalox and its Peridiem laxative and Ascriptin coated asprin with Ciba's Acutrim diet pills, Fiberall laxatives, Efidac nasal spray and Doan's pills for back pain.

Robert E. Cawthorn, chairman and chief executive of French-owned Rhone- Poulence Rorer said the company has decided it doesn't have enough non- prescription products or sales in the United States and Canada to remain competitive, although it remains the No. 2 over-the-counter drugmaker in Europe.

''Today's agreement gives good economic value to RPR and its shareholders for the U.S. and Canadian OTC business,'' said Cawthorn.

The purchase adds to previous Ciba acquisitions in North American products and gives the company ''the critical mass to become a major player in this important market,'' Roland Jeannet, the head of Ciba's over-the-counter drug division, said in a statement from its Basel headquarters.

Peter Mayer, head of New Jersey-based Ciba Consumer Pharmaceuticals, said the transaction moves the company into the top 10 over-the-counter firms in the United States.

The company said the new additions are expected increase sales by $160 million for the Ciba Self-Medication division, which in 1993 had worldwide sales of $640 million.

Included in the agreement is a production plant in Fort Washington, Pa.

The business being sold employs 480 people, most at the Pennsylvania plant. Ciba said it has committed to hiring 360 people and will make decisions on the job status of the rest by the end of January.

The purchase is subject to U.S. and Canadian government approval.

RPR's U.S. shares gained 25 cents to $37.12 1/2 in early trading on the New York Stock Exchange. Ciba shares aren't traded publicly in the United States.