Genex Corp. reported a third-quarter loss of $2.2 million (17 cents a share), compared with a profit of $3.7 million (29 cents) in the like period last year. Third-quarter revenue dropped to $4.6 million this year from $12 million in 1984.

The Rockville biotechnology company attributed the results to "a substantial drop" in the price paid by G. D. Searle & Co. to Genex for L-phenylalanine, an amino-acid ingredient in the low-calorie sweetener aspartame. Sales of the substance have accounted for 87 percent of Genex's revenue this year. Genex also said the results for the third quarter of 1984 were inflated by a one-time payment of $6.9 million.

Searle said in June that it would not renew Genex's supply contract after it expired Oct. 31. Genex said earlier this week that it has sued Searle for more than $40 million for reasons stemming from Searle's decision.

For the nine months ended Sept. 30, Genex reported a loss of $6.9 million (54 cents), down from net income of $79,000 (1 cent) in the comparable period of 1984. Revenue declined to $14.3 million this year from $25.3 million last year.

*Bank of Virginia Co. reported an 18 percent increase in third-quarter net income to $11.1 million (86 cents) from $9.4 million (74 cents) in the same period of 1984.

For the first nine months of the year, profits rose 19 percent to $32.3 million ($2.51) from $27 million ($2.14) last year.

Frederick Deane Jr., Bank of Virginia's chairman and chief executive officer, said the earnings reflected higher levels of loans and other earning assets and growth in non-interest income.

Bank of Virginia's total assets on Sept. 30 were $4.5 billion, up 13 percent over $4 billion a year before.