Genex Corp. said yesterday it has eliminated 54 research and administration positions, or about 16 percent of its total staff, because of a "presently declining cash position."

All of the layoffs, which took effect yesterday, affected employes in the Rockville company's local facilities. The cuts did not affect any employes at Genex's production plant in Paducah, Ky.

The Paducah plant recently started production of the amino acids used by G. D. Searle & Co. to make the low-calorie sweetener aspartame.

Genex President V. M. Esposito said the layoffs were necessary because the Pacudah plant start-up costs have been "substantially higher than expected." Equipment costs, in particular, were much higher than anticipated, said Shellie Roth, the company's spokeswoman.

In addition to its aspartame-related products, Genex sells an enzyme-based drain cleaner and is working to develop novel ways to produce enzymes for food processing and vitamins.

"The steps we have taken today to ensure efficiency will not affect the timing of those products coming to market or the delivery of research and development services to our clients," Esposito said.

Genex reported its first profit in this year's third quarter. The firm earned $3.7 million on sales of $19.3 million, but attributed the profit to a $6.9 million nonrecurring payment related to the termination of a joint research agreement with Allied Corp. Genex said it expects to report "substantially lower" sales and a net loss in the fourth quarter.