The chemical accidentally released at a Union Carbide factory at Institute, W.Va., though closely related to one of the most potent pesticides known, is far less dangerous, according to studies conducted by the company and filed with the Environmental Protection Agency.

The leaked chemical is aldicarb oxime, a less toxic substance treated with methyl isocyanate (MIC) to make the far more potent pesticide called aldicarb. MIC, the chemical that killed more than 2,000 people when it leaked from a Union Carbide plant in Bhopal, India, last December, was not involved in the Institute incident.

Although toxic substances work in many different ways to produce their effects, all can be compared roughly using a test in which the substance is fed to laboratory rats at steadily increasing doses until half of the animals are killed.

According to this test, called LD-50 for the lethal dose affecting 50 percent, aldicarb is 2,400 times more toxic than aldicarb oxime, the leaked chemical. On the same scale, aldicarb is 70 times as toxic as MIC.

According to data provided by an EPA spokesman, the leaked chemical causes blurred vision, watering of the eyes, dry mouth, dizziness and irritation of mucous membranes of the nose and mouth.

Industry sources say Union Carbide is the only known manufacturer or user of aldicarb oxime. It is used as a precursor in production of aldicarb, a pesticide sprayed on cotton fields and certain other crops to kill nematodes, tiny worms that live in the soil and attack plant roots.

Aldicarb, sold under the brand name Temik, can be fatal to humans.

When absorbed through the skin, it interferes with the nervous system, blocking certain chemical reactions necessary for nerve cells to transmit signals from one to another.

The effects begin as twitching and progress to numbness, paralysis, coma and death.