Here's a pop quiz about contemporary advertising: When that luscious Swedish model was urging you to "Take it off, take it all off," what product was she pushing? The half-clad young woman kneeling at the edge of the brook represents what brand of soft drink? Which country does the sultry bathing beauty standing thigh-high in the ocean want you to visit?

Two university professors will be surprised if you remember: Noxzema shave cream, White Rock beverages and Jamaica. They have recently completed an experiment to determine whether sex in such advertising really sells. Their answer: usually only itself. "People remember a nude," says M. Wayne Alexander, 39, chairman of the business administration department of Moorhead State University in Minnesota, "but not the product she's selling." Adds his collaborator, psychologist Ben Judd, 35, "The point is that advertisers have to be very careful not to distract their audiences."

The two academicians designed test ads for fictional but commonplace products (like radios), using professional models in the buff. They showed the ads plus others with pastoral backgrounds to 181 male students (and similar ads later to women).

The men liked the nudes, the women didn't, but neither was successful at recalling the product being advertised. In the first study, for example, about 40 percent of the group totally forgot its name. By contrast, everybody remembered it in the pastoral ads.

The nudes in the test were all women "because male nudity still shocks us," Alexander explains, "and we might get a reaction based on pure shock. We're taught that male nudes are not pretty."

Unofficial reaction from feminists to the study has been mixed. Some cheered, saying, "Tell the world that nudity doesn't work," Alexander recalls. "Others said we shouldn't even be doing the research." The morality of using women's bodies to sell products isn't the issue, he insists. "Models do it voluntarily and are well paid. It's a real question whether the advertising industry is exploiting them or vice versa." The ideal ad, he believes, would have no people at all, since they are distracting, clothed or not. There is an obvious exception: "People products," he says, "need people in the ads."

A Texas native, Alexander earned bachelor's and master's degrees in business at California State University at Fresno, then took his doctorate at the University of Illinois. He acknowledges that companies and ad agencies may already have done research on sex in advertising, but points out that "it is client-directed, not academically based, and the results are not available to the public." Colleagues have been helpful in supplementing Alexander's collection of girlie ads (often with a smile). His wife, Carol, a medical technician, found a prize specimen: a three-dimensional promotion poster of voluptuous Dolly Parton.

Alexander and Judd will next try to design an ad using nudity that is effective. They believe the product name should appear over the breast area, about one-third of the way down the page, with the model's hand directing the reader to additional ad copy.

Regardless of the success the two professors have, Alexander says what a model is or isn't wearing is unlikely to affect his own buying habits. Is he academically immune? The answer is more practical. "My wife," he explains, "does most of the shopping."