Facing a public health menace hauntingly similar to the Kepone in Virginia's James River in 1975, officials here are trying to figure out how to dispose of at least six tons of two obscure but highly toxic industrial chemicals.

The chemicals, hexachlorocyclopentadiene (HCP) and a related chlorinated hydrocarbon, octachlorocyclopentene (OCTA), were discovered in the Louisville sewer system March 29 after workers at the main treatment plant began complaining of skin rashes, nausea and loss of memory - all symptoms of exposure to the substances.

HCP, apparently slightly more toxic than OCTA, is a constituent of Kepone, which was blamed for worker sickness and pollution of the James River near Hopewell, Va., nearly two years ago.

HCP is primarily an ingredient in pesticides, resins, dyes and flame-resistant fabrics. Its chemical sidekick, OCTA, is a manufacturing byproduct that is not generally sold.

Some of the products chemically fathered by HCP are endrin, chlordane, Kepone, heptachlor and Tris. Tris is a flame-retardent used until recently in children's sleepwear; the other four are insecticides.

If the chemicals' names are familiar, it may be because all five have been indicted by the Environmental Protection Agency or the Consumer Product Safety Commission as carcinogens - cancer-causing agents.

HCP itself has not been identified as a carcinogen, according to EPA chemist Ralph Jennings, but apparently no one has studied whether it is the origin of the sinister strain in some of its offspring.

Thirty-two workers in Louisville have been treated for symptoms apparently caused by breathing fumes of the HCP and OCTA. Officials say none suffered serious injury.

The discovery of the chemicals forced the closing of the city's main sewage treatment plant, the third largest along the 981-mile Ohio River. Since March 29, an estimated 100 million gallons of untreated sewage has been pumpedinto the river daily. THe dumping will continue for weeks, at least. Federal and state officials are investigating how the chemicals got into the sewer system.

A major factor in the banning of the HCP-fathered pesticides was the very quality that made them valuable in destroying insects: they are unusually stable, lingering for years in soil or water without breaking down. That stability makes their destruction that much more difficult and expensive for Louisville.

While Louisville health officials hurry to devise a strategy for removing the chemicals from the city's treatment plant and sewer lines, officials in Virginia admit they still haven't seen the last of the Kepone discovered in Hopewell's sewer system two years ago. After listening to an account of Louisville's disposal plan, James Saunders, industrial hygienist for the Virginia Department of Health, said: "Well, best of luck, but I don't think it's going to work."

Louisville's latest removal-cost estimates range from $4 million to $7 million. About 60 tons of contaminated grit must be removed from the system and transported to landfills or to a special high-temperature incinerator on the waste disposal ship Vulcania in the Gulf of Mexico. Officials must first locate about 75,000 55-gallon drums, and arrange to have them carried, probably by rail, to the disposal sites.

President Carter has assured local officials that the federal government will share the disposal cost.

The first goal is to clean out the treatment plant, so that it can be returned to operation by the first week of May. Officials have determined that it must be operating by then to prevent a major health hazard related to the flow of so much raw sewage into the Ohio.

The plan is to remove all 27,000 tons of sewage and then flush out the plant with industrial detergents. The sludge and the detergent must be stored for safe disposal later.

When that is done, officials can attack a 20-block-long portion of sewer line, big enough to walk through which they believe carried the chemicals into the treatment plant. Officials plan to flush the blocked-off line with isoproply (rubbing) alcohol and filter in through an activated carbon "dam" to remove, hopefully, the HCP.

Officials hope this operation will be completed next weekend. But it is a more complicated process than it seems. The project will require the cooperation of the weather; rain runoff would fill the sewe line. Because the rubbing alcohol can be flammable, fire engines will stand by; carbon dioxide will be pumped into the sewer line to reduce the likelihood of fire.

Nobody knows whether this strategy will be successful. Arguing against it is the fact that the sewer line, about 70 years old, has a layer of sludge that ranges from eight to 17 inches thick, and HCP, a heavy substance, tends to collect in low spots.

According to Virginia officials, such low spots in the Hopewell sewers still contain Kepone after two years. Hopewell officials pumped Kepone from their sewers into a large lagoon nearby, where it remains today (through some had dissapated). The city is now building a giant incinerator capable of rendering the Kepone harmless.

Chemically, HCP is derived from common substances, crude oil and chlorine.

Bicyclopentene, produced in the refinery breakdown of petroleum, is combined with chlorine, and the result is another jaw-breaker, decachlorocyclopentadiene. That chemical is then broken down into HCP and the other villain in the Louisville sewer story, OCTA.

OCTA has few commercial uses. It is separated from its more versatile and volatile brother by distillation, the same process used to make whisky. HCP, like bourbon, passes out of the distilling chamber as a gas and is condensed into liquid outside. OCTA, like the dregs of the mash, is left in the vat.

In its pure form, HCP is a pale yellow liquid at room temperature, nearly twice as heavy as water.

It has so many uses," said EPS's Jennings, "and it is relatively easy to make in batches."

But occasionally, he said, something goes wrong and a bad batch results - usually half HCP and half OCTA. That, according to EPA analysis, is the makeup of the chemical illegally dumped into the Louisville sewer system.

Only one company is listed in common chemical manufacturers' guidebooks as a major current producer of HCP - Velsicol Chemical Corp. of Chicago, which produces the material in Memphis.

Hooker Chemical Corp. of Niagara Falls, N.Y., has said it quit production in January "for economic reasons."

Indiana authorities confirmed last week that a 58,000-gallon mixture of waste oil and HCP was found on property owned by Kentucky Liquid Recycling, Inc., in New Albany, Ind., across the Ohio River from Louisville.

And federal and state officials have also said they suspect the firm received the HCP from Chemdyne Corp., a waste-disposal firm in Cincinnati, which had obtained it from Velsicol in Memphis.

But thus far no officials has publicly linked Louisville's HCP with that stored in New Albany, which is not connected to the Louisville sewer system.

A check of industries and warehouses along the 20-block sewer line turned up no record of receiving, handling or storing HCP.

For Velsicol, federal investigations have become almost routine. The company was the sole producer of Tris, banned earlier this month, and of the insecticides chlordane and Heptachlor, partially banned in 1975.

EPA investigators blamed a discharge of endrin by Velsicol into the Memphis sewer system for massive fish kills in the Mississippi River in the mid-1960s. The company denied responsibility.

Velsicol now is involved in controversies over two other pesticides it has produced in Bayprot, Tex. - leptophos (Phosvel), and EPN. Investigators charged that both pestcides produced nerve damage in people exposed to them, including plant workers. The company still produces EPN. It quit making leptophos, never licensed in this country and blamed last year for the deaths of a number of Egyptian farm workers.