The country's most widely used dry cleaning fluid causes cancer in mice and may be a danger to 100,000 workers, as well as patrons of the nation's 18,000 coin-operated cleaning shops, the National Cancer Institute will report soon.

Dry cleaning spokesmen maintained yesterday that the only practical substitute for the chemical - perchloroethylene, or "pere" - would be barred from wider use in most cities by fire codes. They called "pere" safe by "any reasonable standards."

"We could wind up with dirtier clothes if we have to abandon it," said Charles Riggott, executive vice president of the International Fabricare Institute.

The NCI findings - to be published in the Federal Register about Sept. 1 - are based on a study in which mice were force-fed perchloroethylene for two years. Of males who lived that long, from 56 to 65 per cent (depending on the chemical's dosage) got liver cancers: of female survivors, 40 per cent developed cancers.

The findings will go to regulatory agencies like the Occupational Safety and Health Administration and Environmental Protection Agency for further investigation and possible action, said Dr. Richard Griesemer, director of NCI's carcinogenesis bioassay program.

"When a chemical is a carcinogen in man, it's also a carcinogen in animals," he said. "So we have to assume that every chemical hazardious in animals is also a carciongen in man until proved otherwise."

OSHA's own laboratory arm, the National Institute for Occupational Safety and Health a year ago reported that mice exposed to large amounts of the same chemical gave birth to off-spring with birth defects. NIOSH recommended that permissible exposure levels for workers be cut in half.

EPA last February issued a report saying the cleaning industry expels 270,000 tons of solvents into the air every year, and there may be a need to curb these emissions to help control air pollution.

But neither OSHA nor EPA has taken any new actions.

"The NCI findings should force them to do so," said Dr. Sidney Wolfe, director of Ralph Nader's Health Research Group. He is a member of an NCI advisory body that voted to recommend that perchlorcethylene "be considered to pose" a cancer-causing risk to humans, although the chemical quickly disappears into the air and is not known to pose any problem to those who wear the newly cleaned clothes.

Officials of the Drycleaning Industry Council and the Dow Chemical Co., which makes the chemical, said:

The NCI study was unrealistic, an argument put forth recently by critics of saccharin studies in which animals were exposed to doses no one would normally encounter.

Dow studies in which rats breathed vapor concentrations three to six times those now permitted in the workplace produced no cancers.

Griesemer called the NCI test method a "standardized, approved one, accepted worldwide."

Rigott and William Fisher, director of the cleaning industry's IFI Research Center in Silver Spring, said there are two other kinds of solvents in wide use - Valclene, fluorocarbon used only for special puropses, and a family of related petroleum-bassed solvents.

The latter group could do the job, but the industry would have to replace 80 per cent of its machines "and that's an awesome financial burden I don't think it could meet," Fisher said. Also, he said, petroleum solvents are used now mainly in older plants and newer fire codes would not permit them.

If there is really no substitute, said Wolfe, ISHA should take other measures to protect workers, for example, "using the chemical only in closed systems," and providing workers protective suits.

It's easy to make such suggestions, Rigott said, "but the costs could make them almost impossible."