By the fall of 1983, the government will begin receiving preliminary data from four major studies related to Agent Orange, according to Dr. Vernon N. Houk, chairman of the government science panel that is monitoring herbicide studies.

Here's a thumbnail sketch of each:

* The Ranch Hand Study is a 20-year project that involves monitoring the health of 1,264 Air Force personnel who flew on herbicide spraying missions. Preliminary data will include physicals and questionnaires about the subjects' health.

* The Vietnam Mortality Study does not specifically have anything to do with Agent Orange, but scientists hope that they can learn general information about Vietnam-era soldiers by comparing the death rates and causes of death of soldiers who served in Vietnam and those who served elsewhere during the same period.

* The Birth Defects Study involves comparing 7,500 babies born with defects to 3,000 normal babies. Interviews will be done to see if any of the children with defects had Vietnam veterans as parents and whether those parents came in contact with Agent Orange.

* The National Institute of Occupational Safety and Health is developing a registry of workers who worked in Agent Orange manufacturing plants to see if they have experienced health problems similar to those reported by Vietnam veterans.