Fernando Aleu, president of Paco Rabanne U.S.A. and the Fragrance Foundation, once arrived in Paris in the middle of the night, hours after his wife had checked into the hotel.He picked up the key at the front desk, and being careful not to wake her, tiptoed into the darkened room. But when he started to undress, he noticed that something was wrong. "She did not smell like my wife," he said, adding that his wife, Nancy, always wears Calandre perfume. He quickly slipped out of the room.

One shouldn't turn up a nose at Aleu's observations on smells. A neuropathologist and professor, a perfume company executive, Aleu helped organize a survey of smell at Georgetown University.

Looking far more the international business executive than a doctor in his dark pin-stripe suit and foulard tie, wearing a barely apparent limey fragrance, Aleu spoke to a group of 50 or so Washington store buyers and sales staff at breakfast at the Madison Hotel yesterday. He teased, flirted, cajoled and informed them about the importance of smell. Among the things he told them were:

In Barcelona, radar traps snare most speeders near a factory that emits bad smells.

Napoleon never braved a battle without dousing himself in perfume.

50 million Americans don't smell anything.

King Tut -- "Estee Lauder's dream man," Aleu said playfully -- was buried with 300 bottles of cologne.

Smell is the neglected sense. "No one ever had a ball for those who can't smell."

Aroma therapy, the current rage in California, probably works.

Aleu is not a man who takes his business lightly. He remembers the debate he had with Margaret Mead at a Fragrance Foundation luncheon in 1976. She said that commercial fragrances had a way of interfering with human messages. To Aleu, these were fighting words. So he undertook his own experiment.

That Friday, he said, he played two sets of tennis, did some gardening, then back to more tennis. Afterward he told his wife, "We'll go to the movies and I will guarantee you there will be an empty seat next to me." The theater was crowded, he said, but no one sat next to him.

Aleu, who studied medicine in Barcelona, interned in Iowa, was teaching at New York University medical school when his boyhood chum and teammate from the Spanish ski team, Mariano Puig, asked to open the market for men's fragrances in the United States. Aleu juggled both his interests by opening the American branch of Puig in New York and retaining a chair as associate professor of neuropathology at Albert Einstein College of New York. He has been with Paco Rabanne since the company introduced its first perfume 10 years ago. This year they are inaugurating a third fragrance, Metal.

Aleu's science background is a natural for a business that prides itself on research -- from "nose" testing the fragrance to packaging to test-marketing the name. Aleu is constantly observing and researching.

Once, at home, he conducted a test on rabbits. One cage was all male, one all female, one mixed. Aleu put perfume between the ears of one rabbit in each cage. "Friends in the cage sniffed, stayed back in awe," he said. "Because of the smell there was a new social order. And the anonymity of the rabbit with the perfume was decreased." Aleu tied the experiment to the "anonymity of everyone who is only a number to his bank, his department store, even his massage parlor."

It's not always the pleasant smells that he notices. He recalled flying back from Europe on one of the "exotic airlines." He sat next to a person who "gave me an olefactory message I did not relish." Aleu raced off the plane and got the last taxi and when the man asked to share a cab into New York, "I changed my moral behavior," said Aleu, who fibbed that he was going to Westchester. "He made a liar of me, and I left him on the cold, rainy sidewalk and he probably caught a cold."

Aleu concerns himself not only with the fragrance one wears but about everything one smells. "Every hotel room smells like a mix of Camay or Dial, plastic tapestry and Mr. Clean. And the Holiday Inn rooms smell the same in Frederick, Md., or Kansas City," he says. "Many people spray their own cologne in their hotel room and suddenly the motel becomes your home. It makes you more comfortable in a foreign environment."

Aleu fights Alex Comfort's conclusion in "The Joy of Sex" that "the natural perfume of a clean woman is her greatest asset after her beauty . . . (and some would say greater than that)." Said Aleu: "The human animal -- and I like the word animal -- has been conditioned by society to particularly dislike these primary smells out of context. You certainly wouldn't want to go to the White House reception smelling like this lady," he said, pointing to an intimate illustration in the Comfort book.

But while he believes perfumes enhance the sexual attractiveness of women . . . "The woman who perfumes herself heavily is not likely to be an ascetic nun at a Benedictine monastery . . . Most men will respond to a woman that exhibits, in a variety of ways, a desire to be attractive. Because of the great evocative powers of perfume, men are almost accustomed, or they expect, that an attractive woman in a romantically propitious moment will wear a fragrance."

But, he admitted, nothing quite attracts like the pheromones, the stimuli that travels through the air and can stimulate sex behavior in bees and moths, for example. There is nothing like it, so far, for humans. "the man who makes that will earn $1 million," he laughed.