Flow General's planned initial delivery of significant quantities of interferon, considered a potential cancer-fighting agent, to the National Cancer Institute this month will be delayed "by some weeks," the McLean-based research company said late last week.

Under the terms of a $2 million-plus contract awarded last year, the company's biomedical subsidiary, Flow Laboratories, is producing 50 billion international units of human fibroblast interferon -- enough for 50,000 doses to be used by the NCI in clinical tests.

Interferon is a natural protein produced by cells to defend the body against disease-causing viruses and cancer cells. The technology used by Flow involves the growth of large quantities of fibroblast cells on the surfaces of small, charged spheres called Superbeads, invented and patented by the Massachusetts Institute of Technology. Because it uses the surface of beads, the procedure allows a large quantity of cells to be grown in a relatively small space. Interferon in produced when the cells are exposed and react to a virus or virus-like substance.

In a report issued to summarize the company's interferon involvement, Flow said ther scale-up program for large-volume systems of cell production progressed at an acceptable rate through December. "Production achievements during this period were such that, in the opinion of the company, the integrity of the basic system was demonstrated," Flow said.

However, more recently, contamination of what Flow called the living cell pyramid was encountered, resulting "in a setback of an indeterminate period . . . which will delay beyond the February target date by some weeks" the delivery of substantial qualntities of interferon under its NCI contract, Flow said.

In issuing the summmary, Flow emphasized the speculative aspects of interferon as a commercial product, noting that its value in treating human diseases has not been established. It also noted that the production methods it is using may prove to be less desirable than other methods under development.

Despite the caveats, Flow's work has been the object of keen interest in medical circles and on Wall Street. Shares of the company, which are traded on the American Stock Exchange, have ranged between 25 5/8 and 36 1/2 over the last 52 weeks. On Friday, as news of the delay in delivery of the interferon spread, the stock fell 2 3/8 to close at 29 5/8 in composite trading.

Flow said in its status report that in addition to its fibroblast interferon development work, it is evaluating a process developed at New York University for the production of gamma (immune) interferon using conventional cells systems. Limited amounts have been produced so far using the process, Flow said, adding that it has certain rights to the system. Although this process is in an early stage of development and its commercial use also hasn't been demonstrated yet, Flow said it believes a number of organizations, including the U.S. government, may be interested in producing sizable quantities of gamma (immune) interferon for futher evaluation.

The company has announced two new agreements. One licenses Sclavo S.p.A. of siena, Italy, to manufacture and sell human fibroblast interferon in Italy and Argentina according to production technology being developed by Flow. A leading center for the study and production of biological products in Italy, Sclavo S.p.A., which is a wholly owned subsidiary of Anic, a member of the ENI group of companies, will participate with Flow in improving the production process. Under the terms of the licensing agreement -- assuming successful completion of the scale-up of the production system under the NCI contact -- Flow will receive periodic payments, and royalities based on Sclavo's net sales in exchange for the transfer of technology. The agreement runs for eight years with two option periods of four years each.

The other is an agreement for a joint program with Mediscience Inc., whose wholly owned subsidiary, Schwartz/Mann, will engage in research and development with Flow aimed at producing for commerical use a product possessing the biological characteristics of human interferon.