Channel 9's Deena Clark, assured by the executive director of the Tourism Association of Canakkale, Turkey, that she was "the only woman to have ever swum the Hellespont" when she emerged from the water on Sept. 7, in fact shares the honor. Florence Chadwick, who also swam the English, and lesser-known swimmers have also made the crossing.

In 19 years of doing the television show "A Moment With . . ." Deena CLark has spent moments with just about anyone Washington could offer in the way of celebrities. But she's been aspiring to move in better circles.

The celebrities she's been after since childhood are Poseidon, Leander and Lord Byron. Early last month, on her 53d birthday, she finally had her moment of glory in association with them.

Leander, you will recall, was the chap who lived on the Asian side of the Hellespont some years ago and was courting a priestess named Hero on the European side. He commuted by water for their nightly assignations until inclement weather and a faulty lighting system put an end to the romance and to him. Hero, being a true heroine, jumped from her tower to her death when she saw his dead body washed up on her shore.

The rest, as they say (in fact, all of it), is legend, Greek legend, which Deena (for Constandina) heard from her Greek father, Christos Aristotles Speliakes. He was a Spartan candymaker - Spartan in the geographical sense rather than the metaphorical. But Clark says she got her athletic inclinations and determination from that heritage.

Clark says it was a lifelong dream of hers to swim the Hellespont like Leander and also, for that matter, like Lord Byron, who did it in 1818 and later wrote. "I would rather have swum the Hellespont than written all my poems."

Last year, she went into serious training for it, at such serious places as the Chevy Chase Club, Washington Hilton and Watergate swimming pools, as well as her native La Jolia, Calif., and the Bosporus. She set the date for Sept. 7, 1977 ("lucky three sevens in a row,") after a more conventional vacation, cruising Greek islands with a group from the Pisces Club.

And she did it, too, in 63 minutes, swimming three miles across the one-mile channel (the modern name of which is Dardanelles) because of the currents.

Lord Byron, in contrast, took 90 minutes. "He wasn't much of a swimmer," said Clark.

The only other documented crossings were Richard Haliburton's, in 1927, and Jack Wheeler's, in 1960.

And Leander's, of course. But Clark no longer believes in him. "He couldn't have done it in the dark," she said. "And if the currents were with him one way, they wouldn't have been with him coming back."

For the occasion, Clark wore a Cole of California bathing suit, Bulgari stud diamond earrings, and St. Christopher medal. At the finish, she was crowned with marigold wreaths by the assortment of friends, Turkish fishermen and the minister of tourism. They also provided champagne and chocolate Birthday cake, which she cut while still in the water.

Unlike Byron, she did not say that she would rather have swam the Hellespont than done all her television shows. But she did say to her assembled admirers. "I'm glad I was born. Otherwise, I would never have been able to make my dream come true. I tasted all the beauties. And I have reached the top of happiness.

"I think Poseidon was really watching over me. I really do. Something was working right. It was 71 unbelievable warm degrees.

"I felt close to my father. I felt close to my childhood. I felt close to my ancestry. It was a marvelous birthday present to give myself."

An early present had been a T-shirt from her daughter, with the words "Whip the Hellespont" on the front and "Deena" with a star on the back. The reference is to the Persian king Xerxes' attempt to whip the Hellespont with chains to subdue a story that interfered with an attempted invasion of Greece.

Clark credits luck - in temperature and currents - as well as Poseidon and herself for her adventure. If she hadn't made it, "I wouldn't have come home until I did," she said in true Spartan tradition.

And what next? Well, she's got her opening television show, now called "The Deena Clark Show," which will appear once a month on CBS; and she's planning to compete in the La Jolla Rough Water Swim next year.

"It's not a dream, like the Hellespont was," she admitted.

One legend to a lifetime.