Pesticides have long been suspected of causing cancer and other serious diseases. New studies lend support to these concerns, linking pesticides to diseases in children and breast cancer in women. The greatest worry is over pesticide residues in food and drinking water. But pesticides also pose a danger to agricultural workers and homeowners who use these chemicals. And runoff from fields pollutes groundwater, rivers and coastal areas, killing untold numbers of fish and animals. Farmers and chemical manufacturers agree with environmentalists and consumer advocates that current regulations governing pesticides are inconsistent, but they differ on a solution. Now the Clinton administration proposes to overhaul the laws regulating pesticide use, and Congress is expected to address the issue this year.