Elwood P. Dowd had Harvey and Art Ulene has Corky.

While Dowd's onstage friends and relatives thought him a bit strange, the people sitting in the audience of the hit play by Mary Chase came to believe in the existence of Harvey as frevently as Dowd did.

When Dr. Ulene, Gynecologist-obstetrician-turned TV doctor, talks about the importance of Corky, his imaginary rabbit, initial skepticism finally gives way to grudging acceptance. But only because the doctor on the Feeling Fine segment of the "Today" show certainly seems to have it all together.

He gives the rabbit some of the credit for his ability to cope with problems that might have sent him up the wall several years ago. Take THE CAR EXPERIENCE. In 14 months Dr. Ulene's car had been in the repair shop 31 times. Instead of kicking in the front end, he consulted Corky, who calmed him down and told him in a very firm voice: "Sell it immediately!"

He did. Smart rabbit.

Dr. Ulene recommends an imaginary companion to help relieve stress and pain in his book, "Feeling Fine" (J.P. Tarcher, Inc., $7.95).The book uses phrases like "guided imagery," "unstressing pleasures," "eating pleasures," but what it really is, according to the doctor is, "a sampler of enjoyable things to do that are good for you."

How does a hyn-ob physician, trained to cure, to operate, to repair, come to write a book which offers seven commonsense rules for living longer?

The author, who seems never to raise his voice, or even boil internally, can point his career to a day four years ago. He was training 21 nurse-practitioners in gynecology and discovered that only two of them were examinig their breasts, a fact he found appaling. "I got very active in motivating them," Ulene said during a recent interview in Los Angeles where he lives. "In 11 years as a doctor with all the fancy operations I had done, the most important thing I had done was to get these women to examine their own breasts. After that I went on a breast self-examination crusade.

"That's when I tried to interest people in television in health education and they said it was dull and people were not interested. I went to the National Cancer Institute for a grant and they turned it down cold."

But someone from another Los Angeles television station was interested in Ulene's idea and together they created a five-minute-a-day, week-long program on breast self-examination. "They printed 2,000 pamphlets to send to veiwers and 100,000 wrote in."

Then the NBC station in Los Angeles asked Ulene to develop a program on other health matters. That was the beginning of Feeling Fine. The first project was a weight-loss program which was shown in 50 cities: 2 million people wrote in for that brochure.

The key to Ulene's success appears to be his ability to make healthful activities, if not actually fun, at least more than just tolerable. For the diet program he asked people to play a game of "collecting points. What we never told anyone was that every point was 28 calories. People love to play games but they hate to count calories."

The "Feeling Fine" book makes a game out of most things. It's as upbeat as the subtitle indicates: "A 20-day program of pleasures for a lifetime of health."

But nowhere in the book does the doctor say it all boils down to: eat three meals a day; stay close to your ideal weight; sleep seven hours a night don't drink more than two drinks a day; don't smoke; be active every day.

According to Ulene, studies have shown that men who do three or more of these every day live 11 years longer than men who don't and women add seven years to their lives.

At 41, Ulene, who was born in Montreal, has already had more careers than most people do in a lifetime. His wife, Priscilla, says it's because he's "hyperactive."

When he was in medical school he ran a day-care center. That's where the Ulenes met. As a resident the started a business which scheduled doctors in emergency rooms. It helped to keep body and soul together on a resident's meager salary. The business became so large that Ulene sold it in 1970 and went to work for the company. But after six months he realized he missed clinical medicine. "I walked away from everything I had believed important: money, position, power and took a cut in pay to one-third of what I had been earning. At the time we were borrowed to the hilt. We gave up the maid, the fancy cars, the fancy vacations. I went back to USC (University of Southern California) full time."

From then until last year he was on the university faculty. As time went by Ulene found he was teaching less and administering more, a job he didn't particularly like. Last fall he left USC and now spends half his time in private practice and half on his Feeling Fine shows in Los Angeles, Washington and San Francisco as well as the "Today" show. He is also working on a pilot for a half-hour health show.

His career changes have affected his family's lifestyle. His wife now works full time - in his Feeling Fine office. His children have become more independent. Ulene has kicked his two pack-a-day-habit and he no longer takes any medication. Instead of vacations lying on the beach, the family sails and skis. Their eating habits have undergone some serious revisions. They've cut way back on meat, use margarine instead of butter, eat a lot of fruits and whole-grain breads.

Some of the dietary changes have rubbed off on the children - to varying degrees, according to Ulene. "They make their own decisions. So one always orders low-fat milk.Another orders it half the time and Coke the other half. The third always orders Coke," he said with a laugh.

But the most important thing according to the doctor is that "I've learned to recognize when I'm under stress and so I don't. I've came to recognize you almost always have a choice: I could have gottens sick over the car, or talked to the rabbit."

Ulene says he's also learned not to expect others to work the way he does. "As long as its reliable, I don't mind if it isn't done the way I would do it."

Priscilla Ulene says her husband's celebrity status, which has meant a loss of privacy, also "makes him act more calmly." It would never do now for him to scream and stamp his feet in public - or kick the front end of his car.

This new position also makes a lot of people want him to be doctor. He won't take him as patients. "People who call because of TV aren't looking for Art Ulene: They're looking for Marcus Welby. These people have unrealistis expectations."

He also won't prescribe long distance. "I'm not psychic. I don't have ESP and I can't treat by mail."

Ulene has conflicting feelings about his effectiveness. "There are times when I get discouraged when I think we are working with a pea shooter."

There are other times when he feels he is "making a dent. Feeling Fine could not have been on the air five years ago. The kinds of letters we get, not only from lay people, but from doctors, who tell me their patients tell them what I've said," show that.

But nobody's perfect. Thank goodness.

There is one situation over which his rabbit has no control. When Ulene finds that there are no copies of his "Feeling Fine" book in a store, he still gets very angry.