Versar Inc., the Springfield environmental services firm, said yesterday that it has signed a letter of intent with an unidentified financial group to sell Gammaflux Inc., its last manufacturing subsidiary not related to environmental management.

Gammaflux, which is in Herndon, makes instruments that control the temperature of plastics as they are injected into molds. That factor is critical to the quality of high-grade plastics, such as those used in cars.

Versar has been planning to sell the subsidiary for about three years, said Michael Markels Jr., company president and chief executive. The sale, for $4.45 million in cash and notes, is part of a streamlining effort at the company, which also has sold some of its smaller environmental subsidiaries.

In a recent interview about Versar, for years a diversified scientific and technical services firm, Markels had talked about the Gammaflux sale.

"Once {Gammaflux} goes, everything else we do is related to the environment," he said. "That will make the difference. We will then be an environmental risk management firm."

The sale of Gammaflux dwarfs Versar's sale of its other non-environmental manufacturing subsidiary last March for about $250,000. Gammaflux, which has annual revenue of about $4.5 million, has been profitable, unlike the other subsidiary. Versar owns 81 percent of Gammaflux; the rest is owned by the firm's management.

Versar's earnings have been disappointing in recent years. In fiscal year 1990, which ended last June, Versar made $41,000 on revenue of $60.9 million. In 1989, the company lost $256,000 on $57.6 million in revenue.