A lot of fingers are going to be crossed in Louisville Sunday morning.

Unless something else goes wrong, the city's main sewage treatment plant, closed since March 29 because of chemical contamination of the sewer system, will be put in operation at midnight Sunday.

During the two months of the plant's shutdown, nearly 7 billion gallons of raw sewage have poured into the Ohio River, at a rate of about 100 millions gallons a day.

Kentucky water pollution officials say the sewage had not threatened the ecology of the river or created a health hazard. But they also say that further delays - into midsummer, when the river is "lowest and slowest" - could lead to limits on fi - and a host of other target dates for reopening the plant have been missed because of dark surprises - not all of the city's sewage will be treated.And what will receive treatment won't be treated fully for several more weeks.

When the plant returns to operation, about 85 per cent of Louisville's sewage will be routed though the plant, according to Metropolitan Sewer District spokesman John Tierney.

The remaining 15 per cent will be routed through the plant after two sewer lines still contaminated with the toxic chemicals have been cleaned and made ready for reconnection to the plant.

The MSA closed the plant after 15 workers were sickened by fumes from at least six tons of two highly toxic chemicals dumped into the system early in March.

The chemicals, hexachlorocyclopentadiene (HCP) and octachlorocyclopentene (Octa), cause rashes and burns and can affect the central nervous system, according to government and industry researchers. They say it has not been determined whether either substance is carcinogenic.

HCP is a reagent used to make pesticides and flames-resistant fabrics. Octa is a byproduct of its manufacture.

MSD officials had hoped to reopen the plan last Wednesday, but they were forced to delay when they found that a sewer line previously thought untouched by the chemicals had a layer of the gooey mixture about five inches thick for 1,400 feet of its length.

But the cleanup of the line went faster than expected. Workers found less of the chemicals than they had anticipated; and by removing a section of a "diversion chamber" connected to the line the eight-foot-wide line, speeding the job.

"Those men also wanted to get the job done," said Tierney after the workers had cleaned the entire 1 1/2 miles during a 12-hour shift."They've been working on this a long time. They really went after it."

The plant employs both primary "physical" treatment and secondary "biological" treatment and wastes.

Only they primary treatment, which involves screening out solid matter and aerating the rest, will be available at the outset. It will take four or five more weeks for the microorganisms that accomplish secondary treatment to become effective, Tierney said. 'The plant's old microorganisms died during the long layoff.

Primary treatment will remove about 60 per cent of the bacteria from sewage. Secondary treatment removes an additional 30 per cent.

The FBI this week arrested two Louisville businessmen, Donald E. Distler and Charles W. Horn Jr., on charges of violating dumping of the chemicals.

The two men are principals in Kentucky Liquid Recycling, Inc., a Lousville firm that handles and store chemical wastes.

Paul Traina, chief of enforcement in the U.S. Enviornmental Protection Agency's Southeast region, said that to his knowledge the arrests were the first under the Water Pollution Control Act Amendments of 1972, the nation's basic clean-water law.