It was hard enough for the commuters streaming down Rock Creek Parkway yesterday morning: There was the U.S. Marine Band drawn up below the Shoreham Americana playing "Vesti la Giubba" at the top of their lungs and all these slims in running shorts lounging around this big green-and-white striped tent.

If you were jogging down in the parkway path it was even worse: Surely that couldn't be George McGovern stepping out of that trailer: And the Boston voice booming across the treetops and causing two bicylists to collide - was it a Kennedy? Yes it was Senator Edward himself, tanned and fit, as they say, and talking about health.

They were celebrating the fact that someone has at least figured out a way to make a buck from jogging without selling clothes or writing books.

Healthy people seem to get up earlier than the rest of us. Certainly the hundred who gathered to dedicate Washington's new Parcourse at 8 a.m. looked healthy. Some of them, like FDA Commissioner Donald Kennedy, were actually dressed in running suits, and you have to be fit indeed to wear shorts on a speakers' platform.

You never saw so many healthy people: Olympic swimmer Donna de Varona, Earl the Pearl Monroe and Kevin Grevey of the Bullets, former Redskins Brig Owen and Larry Brown, Boston Marathon champion Bill Rodgers - plus a platoon of huge Marines with scalplock haircuts and pretty people in Healthy America sweatshirts. You couldn't see two pounds of fat in the whole group, not counting the press.

After the speechmaking they went through the 1.5-mile course laid out along Rock Creek.

The Parcourse is the first of 200 being donated to the nation by the Perrier Water Co. Bruce S. Nevins, president of Perrier, was on the stand as was the president of Dannon Yogurt, Juan Metzger, demonstrating solidarity for great bodies. "People who run are our crowd," Metzger said.

You never heard of a Parcourse? The idea was imported from Switzerland in 1973 by San Francisco businessman Peter Stocker. A Swiss life insurance firm had put up these calisthenics stations as a public service during the '50s, and Stocker liked them so much he formed Parcourse Ltd., and built 200 courses, in 30 states.

Colleges go for them, corporations love them, heads-up developers see them as a drawing card, and now the National Park Service is getting a lifetime supply.

The course, which has to be the most imaginative means yet devised for capitalizing on America's jogging craze, consists of 18 stations, each featuring a billboard and some sturdy simple wooden equipment. Thus sating both our hunger for instructions and our thirst for gadgets. But fanatical runners may not find paradise at the Parcourse. "It's a good course especially for running a mile or so," said Tinley Roughton, president of RunHers, a women's running club, "but I am a pretty serious runner and refer not to stop when I am running."

The first exercises aim to stretch and loosen muscles, the middle ones get to work on legs, back and arms, and the last ones cool down the enthusiast, who is encouraged to jog from one station to the next.

Exercises range from toe-touching and knee lifts to pushups and situps.

"Everybody likes the idea," says Parcourse sales manager Richard Cunningham in San Francisco. "We hear nothing but nice things about it."

The firm is building about 12 courses a month, he said. Materials and labor cost $5,850, and for $7,500 you can get a prefab course installed. By September New York City should have three units operating.

Back at the dedication ceremony, Sen. McGovern (who is on the board of Healthy America and heads the Senate Subcommittee on Nutrition) talked about "the relationship between what we eat and what we are" and said that six of the 10 leading causes of death related to diet. "We are what we eat," he said.

Nevins, Dr. Charles Arnold and American Medical Association President Dr. Tom E. Nesbitt were among the speakers who were already in town to attend the Healthy America conference today at the Shoreham. But it was Kennedy, chairman of Healthy America's board of advisers, who made heads turn when he arrived in a big black limo.

"Only two cents of our health dollar go to keep people healthy," he said, and all we need is something like the Parcourse to help people work harder to keep healthy. He credited the new national awareness about nutrition and exercise with helping bring down the rate of deaths from strokes 40 per cent in the past five years.

It was 9:30, and the speeches were finally over. Kennedy cut a red ribbon and the celebrity joggers attacked the Parcourse in groups of six.

But celebrities in running shorts look just like anybody else in running shorts. The commuters still streamed past, but there were no more doubletakes. The Parcourse had joined the Washington scene.