WHEN THE Lou Ferrigno "Hercules" (already known in some circles as "Hulkules") was unleashed on an unsuspecting world last week, it had one--and just one--redeeming quality. It made you realize just how good the 1959 original was.

And Steve Reeves, the man who flexed his mighty muscles there and in a dozen other films, is still in remarkably good shape at age 57. It's not hard to see what made him progressively Mr. Pacific, Mr. America, Mr. World and, finally, Mr. Universe.

Reeves was recently the cover story on "Muscle and Fitness" magazine (they did a 25-page spread on him), and he admits that keeping in shape is very important to him. "If you want to be an example, you have to. I enjoy being fit, it's a good feeling," he said this week at his ranch about an hour north of San Diego.

Even in slightly ridiculous action films such as "Hercules," "Hercules Unchained," "Thief of Baghdad" and "Goliath and the Barbarians," Reeves was somehow believable, certainly the most believable of all the musclemen who made it to the big screen.

"I tried to do my parts as true and sincere as I could and put as much into them as I could," he said. "When I look at the films I did, they seem to have weathered the time very well. When I was doing them, I didn't think too much of my acting, but as I see them now in retrospect, I think, 'You weren't such a bad actor after all.' And when I did my feats, it looked like a man of superhuman strength doing a feat, it didn't look like a fake or a special effect."

Born in Glasgow, Mont., but raised in Oakland, Calif., he said he was a pretty regular kid until he got a heavy balloon-tire bicycle at 13. "I used to exercise by riding up and down the hills. By the time I was in junior high school, my legs were in really good shape and my upper body was about average. I was also fairly strong because I could beat everybody in my school wrist-wrestling. But then I decided I should develop my upper body to match my legs."

He began at age 16 with a small set of weights found in the high school gym.

"I liked the feeling so I went to a professional gym and started exercising there. It was really easy for me and I made fantastic gains--30 pounds of solid muscle in three months."

After winning the Mr. Universe mantle in 1950, Reeves dropped out of competitions and, in 1954, appeared in his first film, a musical comedy called "Athena."

Reeves describes it as "the adventures of a Mr. America who was being trained to be Mr. Universe by Louis Calhern, who had named all his granddaughters after Greek goddesses --Athena, Minerva, etc. He had them on health food and exercises and he wanted Athena--Jane Powell--to marry me and raise a superfamily."

The film also featured Vic Damone, Debbie Reynolds, Edmund Purdom and Linda Christian.

Most of Reeves' films were period pieces, but in this one, "though the girls wore Greek-type costumes, us guys wore Levi's and T-shirts. During the time I was making films, I only exercised with weights once a year, in April, to get ready for my first picture in May. Just the action I did in the films kept me in good shape."

The "Hercules" films inspired a host of bad imitators in the early '60s ("Hercules Against the Moon Men," "Hercules and the Captive Women"), as well as inspiring many youngsters to take up muscle building ("Ken Norton told me he used to sneak out of school to watch me"). One of those, of course, was Ferrigno, whom Reeves has only met once. Reeves hasn't seen the new version ("Hasn't gotten to my neighborhood yet").

Reeves recently became a successful author. His "Power Walking" is into a second printing, with a third scheduled for this month.

"It's an aerobic walking technique that I developed quite accidentally. I have Morgan horses here, and one time I was leading a trail ride that lasted about 26 miles. Some of the people hadn't ridden for a while and the horses weren't in too good shape, so I thought we'd use the cavalry style, where you walk beside the horse for 10 minutes out of every hour.

"When I got off my horse, he started walking away from me, so I started stretching out my legs, increasing my stride and catching up. Then I started swinging my free arm--the other was on the bridle--in a pendulum-like motion and I was catching up real good. When I started getting breathless, I started breathing in three breaths and out three breaths in rhythm with each three steps. And it seemed to work real well. When I looked back, the rest of the people were way in the background and I thought, hey, this is a great cardiovascular exercise because it doesn't hurt your joints.

"I started developing it from there, adding light handweights. Then I developed weights for the waist and the ankles. I've been doing it for 10 years now and keeping in great shape."

The book project evolved out of a casual party conversation with James Michener. "He said, 'Why don't you write a book?' I said I'm not really an author, but he said to write one page a day for a year and I'd have it made. And that's what I did."

Reeves lives with his wife of 20 years, raising avocado and orange trees and the Morgan horses. "We also have our own organic garden. It keeps me busy. We live a good life."