For months, pesticide production workers at an Occidental Chemical Co. plant in a small central California town had wondered why none of them had fathered any children recently.

Then medical tests were made and two-third of those tested in the plant's pesticide formulation unit were found to be partially or totally sterile.

Now the company has voluntarily shut down the 26-worker unit and, in cooperation with state and federal authorities and union officials is trying to find the cause.

"At this point we just don't know what the cause is," said James Lindley, western division manager for the Occidental Petroleum subsidiary that operates the 350-worker plant in Lathrop, a San Joaquin Valley farm community about 65 miles east of San Francisco.

Lindley said 10 of 15 men tested in the pesticide unit earlier this month were found to be totally sterile or with sperm counts sufficiently low to make conception unlikely. He said most of the men are in their 20s and 30 and had fathered children before taking jobs at the plant.

The tests were made by the company after the Oil, Chemical and Atomic Workers union, which represents workers at the plant, made initial studies that raised questions about the men's fertility.

According to state officials and a union industrial hygienist, a prime suspect as cause of the sterility is a [WORD ILLEGIBLE] known as DBCP (dibrome chloro propane).

William Steffan, head of the occupational health branch of the California Department of Health, said medical evidence "focuses strong suspicion that . . . DBCP is implicated" in sterility. Rafael Maure, Denver-based hygienist for the union, said tests conducted jointly by the University of California and Dow Chemical Co. in 1961 showed that the compound produces sterility in rats.

Neither federal nor state authorities have set standards for worker exposure to DBCP which is reportedly also produced by other large chemical companies.

Lindley said there is no reliable evidence that DBCP caused the workers' sterility and noted that 200 different compounds are produced or mixed for marketing by the unit, which is housed separately from the main fertilizer-producing plant. He said the unit stopped mixing DBCP about two years ago.

It is not yet known whether the sterility is temporary.