There are a lot more women, it seems, who can be talked into the advantages of taking aerobic dance classes, exercising, pumping weight machines, and otherwise using a health club than there are male membership prospects. But, the U.S. Court of Appeals in Cincinnati recently had to decide, is that factual difference a legal difference?

The answer has a lot to do with how effective a weapon the Equal Pay Act will be for women trying to boost their earnings.

That statute makes it unlawful for an employer to pay men and women differently for the same work, but then goes on to say that the precept need not apply if the difference between pay for the two groups is "based on any other factor other than sex."

Ten years ago, in a ruling generally taken as the gospel on the issue, the U.S. Court of Appeals in Philadelphia said that it was okay for the Robert Hall clothing chain to pay male sales clerks--who sold men's clothes--a higher commission rate than was given to the women who sold women's clothes. The rationale: the men's clothing produced more profit for the stores, so the higher commission was tied to the "economic benefit" Robert Hall reaped from the salesmen's efforts, and that was a "factor other than sex."

Using that decision as a guide, a chain of mid-Western health clubs also adopted a commission structure that paid higher commissions to men managers--who ran the clubs on days they were open to males--than to women managers, who ran the facilities on the alternate females-only days. That's because the men customers were a lot fewer. In fact, the women sold roughly three memberships for every two the men sold. That made up for the difference in commission rates, and left male and female managers with about the same dollar pay.

But the judges stil called it a violation of the Equal Pay Act.

The Robert Hall precedent does not apply, the July 11 opinion in Bence v. Detroit Health Corp. explains, because the two groups were selling not different sorts of merchandise, but exactly the same thing. The women made more sales, thereby providing a greater "economic benefit" to the chain, so the company can't use that difference as an excuse to compensate the women less per sale.

But an outsider suspects that the real difference is not that between clothing and club memberships, but between 1973 and 1983. Established, traditional, accepted differences between the treatment of men and women in the workplace just are not as accepted now, and it is that unstated message in the ruling that promises to give the Equal Pay Act some new clout.

In other cases, courts ruled that:

* It can be fraud to sell a house without revealing that it was the site of a grisly murder some years earlier. A California Court of Appeals told the buyer that she could go ahead with her suit to either void the sales contract or get back part of her purchase price once she discovered that four children and their mother had been murdered in the house a decade before the sale. The buyer claimed that the bad reputation decreased the value of the property by about 15 percent. The judges said that if this is so, the sellers had a duty to reveal the unsavory history, just as they would have a duty to reveal a hidden physical defect.

(Reed v. King, July 21)

* Strikers may at times receive unemployment compensation. The West Virginia Supreme Court overturned its precedents holding that strikes are not the kind of unemployment covered by the payment scheme and decided that under some circumstances, those that walk off the job are eligible for benefits. The circumstances: when workers are "compelled to strike because their wages and conditions are substantially less favorable than others in the area" or because their employers have in some other way treated them unfairly.

(Belt v. Cole, July 8)

* Workers and their unions have no legal standing to challenge a plan to improve plant safety conditions once a company and the Occupational Safety & Health Administration agree on the scheme. The U.S. Court of Appeals in Manhattan noted tht employes can have a voice in setting OSHA rules and in kicking off investigations, but the judges found that enforcement is really up to the agency. Letting unions contest a fix-up settlement would actually work against safety, the opinion says, since it would delay implementation of the improvements.

(Donovan and Mobil Oil v. OSHRC, July 17)

* A company officer can be liable for not paying corporate taxes even if he was following his boss's specific instructions. The U.S. Court of Appeals in New Orleans upheld the government's claims against the treasurer of a company that had not sent to the Treasury tax payments withheld from employes, even though he had written company checks covering some of the taxes due and was forbidden by the corporate chief executive officer from paying any more back taxes. The treasurer eventually resigned and told the Internal Revenue Service about the taxes due, but that did not rid him of his legal responsibility for paying the taxes while he held office, regardless of the CEO's instructions to the contrary, the judge ruled.

(Howard v. U.S., August 12)