The Senate Agriculture Committee is set to try once again to overhaul the nation's main law regulating pesticides and fungicides, which many critics contend is virtually useless legislation.

Pesticides are a $5 billion-a-year industry. Tomatoes, beef, potatoes, apples, pork and many other foods arrive at the dinner table laden with chemicals. In a number of states, pesticides have been found in groundwater, often used for drinking.Chemical makers contend that the benefits of pesticides outweigh the risks. They say drinking a glass of well water where contamination has been measured poses less hazard than downing a shot of vodka.

However, there are some 113,000 cases of pesticide-related illness and injury logged each year. A May 1987 National Academy of Sciences report said cancer is caused in laboratory animals by 30 percent of the insecticides most likely to show up in food, 50 percent of the herbicides and 90 percent of the fungicides.

Congress has moved fitfully at best to tighten regulation of the 1 billion pounds of pesticides sprayed on U.S. fields annually in the war on bacteria, fungi, bugs, worms, mice and other forms of crop blight.

Critics ridicule the Federal Insecticide, Fungicide & Rodenticide Act, or Fifra, as hopelessly toothless. We call it a no-law law because it doesn't do anything, consumer advocate Ralph Nader says.

A 1972 rewrite of Fifra gave the Environmental Protection Agency until 1975 to complete a reregistration process, including a full-scale safety review, of some 700 pesticides. In 1975, lawmakers approved a one-year extension. In 1978, the deadline was junked altogether.

The General Accounting Office, an investigative arm of Congress, estimates that at the current pace, the job won't be completed until the year 2024.

Senate Agriculture Committee Chairman Patrick J. Leahy has proposed a nine-year deadline for the reregistration process, plus a possible two-year extension.

I think most Americans are willing to put up with a spot on their lettuce or a blemish on their apple rather than risk cancer, said Mr. Leahy.

The National Agricultural Chemicals Association, champion of the nation's pesticide makers, has no objection to a speedup in itself.

More complex issues, however, are lying in the legislative weeds and could rise up to scuttle the bill. Something similar happened in 1986 when a seeming compromise came unglued just before Congress adjourned.

Chemical companies are willing to contribute to the costs of reregistration by paying $150,000 per ingredient. But the Leahy-Lugar bill calls for $750,000, which the NACA calls A money grab, pure and simple.

Under current law, companies are entitled to indemnities from the Environmental Protection Agency to compensate for the banning of their products. Already the agency has paid $2.4 million to chemical makers for taking the pesticide ethylene dibromide, or EDB, off the market and $18 million for a chemical known as 2,4,5-t, or silex.

And the agency estimates it will pay out between $60 million and $155 million in indemnities and disposal costs to get rid of a pesticide called dinoseb. The annual budget of the entire EPA pesticide program is only $70 million.

The Leahy-Lugar bill would bar such indemnities unless Congress passed an individual money bill for each one. Such a measure is guaranteed a rough time on Capitol Hill. The industry is firmly opposed.

Manufacturers have other objections as well, especially to an amendment Sen. Leahy cosponsored with Sen. David Durenberger, R-Minn. NACA President Jack D. Early told the Agriculture Committee that the Leahy-Durenberger amendment contains an unrealistic groundwater definition, unenforceable goals for water quality standards and (an) unworkable state ground and surface water protection program.