Flow General Inc., a McLean-based research company, has won a contract worth approximately $2 million to produce the potenial cancer-fighting agent inteferon for trials by the National Cancer Institute.

Under the terms of the contract, Flow General's wholly owned subsidiary, Flow Laboratories Inc., will produce 50 billion international units of human fibroblast interferon -- or enough for an estimated 50,000 doses.

Interferon is a natural protein produced by cells to defend the body against disease-causing viruses and cancer cells. Although its medical value is not yet proved, its potential has excited researchers for several years.

The National Cancer Institute hasn't decided where the clinical tests will take place, what types of patients will be used or other details of how the trials will be conducted according to a spokeswoman for the NCI.

The tests will be in two phases, one to establish proper dosage levels for interferon and the other to determine its medical effectiveness at the dose level, according to Dr. Saul Schepartz, deputy director of the treatment program.

Either two or three types of interferon will be tested, depending on whether a third type can be acquired. The institute already has signed an $895,000 contract with Warner-Lambert for 50 billion units of leukocyte interferon.

Full-scale production of interferon by Flow is scheduled to begin in June 1980 and to continue through June 1981. Actual clinical trials of the drug are expected to begin in the fall.

Fibroblast interferon is produced by growing human cells on surfaces and then exposing the cells to a virus or a virus-like surface.

Flow produces interferon on the surface of beads, a process which allows a large quantity of cells to be grown in a relatively small space, producing cost savings.

"If you think in terms of having a container like a coffee cup, the surface available is not very large," said Joseph E. Hall, president of Flow General.

"If you were to fill the cup with marbles, you would greatly increase the surface available," he said. Flow uses a patented process employing cellulose-type beads on which to grown interferon. The process was invented at the Massachusetts Institute of Technology.

Up until now, Flow has produced only laboratory quantities of the drug, Hall said.Hall said the number of uncertainties still attached to the prospects for use of interferon make it hard to predict what impact development of the drug have on Flow's long-range future.