"You are showing you are ready to put your body in a physically strenuous situation for this issue," said Iceland's Gudrun Agnarsdottir, 42, a newly elected member of the Icelandic Parliament, who will participate in the 20th Anniversary March on Washington for Jobs, Peace and Freedom here today. "It's also to strengthen the peace movement in this country and to strengthen the people on the march. Once you're on a peace march, you're never the same. It changes you. It's a fantastic experience."

Gudrun is one of a group of mostly women from six Scandinavian countries who are in the United States to march for peace, to walk down sidewalks and streets between New York City and Washington, D.C., to carry their banners and viewpoints decrying the build-up of nuclear weapons.

And what have they found?

In America, when you're walking, everyone else has a car.

"It's dangerous to leaflet, you know," said one marcher. "It's bad for commmunication."

But it's good for attention--which is the simplest of their reasons to march for peace.

"It impresses Americans to see us walking," said Lise Host-Madsen, a 44-year-old Danish nurse who is active in Denmark's peace movement.

"Some people get angry," said 29-year-old Viveka Englander. "They say, 'Go to Moscow to talk about peace.' " The Swede grinned delightedly. "When we say, 'We were there last year,' they are so surprised."

A 300-mile peace march is like a cross between a swim of the English Channel and a survival-testing session of Outward Bound.

"I've been thinking about Moses walking through the desert," said Eva Nordland, 62, of Norway. "We are thrown together and we have to make peace with each other."

"You're thrown in with thousands of other people you've never known," said Gudrun. "You live very closely with people. You queue for brushing your teeth, you queue for a cup of coffee."

As insurance against emergencies, the marchers are trailed by a rented bus, which picks up weary or injured marchers. There are rest intervals every hour. No one is made to feel ashamed for stopping or not walking that day, and some are reminded that there are support functions that are just as important as the actual walking. Marchers emphasized that strength had to be conserved for other activities, such as the evening meetings and programs in cities along the route.

But many of the marchers appear to be in terrific shape, reinforcing the image that Scandinavians are healthy people.

For marching, they wear soft, thick-soled shoes, usually gym shoes--and most declined to identify the brand, or "mark," as they called it. "That's an advertisement," said Englander.

Few strolling the grounds of the Cedar Lane Unitarian Church in Bethesda, chatting and eating dinner, admitted to any problems. Twenty-nine-year-olds walk alongside 60-year-olds. Dagmar Fagerholt, 71, a longtime Danish peace activist, walks in low heels. Lise Host-Madsen says, "I'm used to it--I'm a nurse."

The tall, wiry woman in the skirt and T-shirt at Cedar Lane was Elisabeth O stberg, 43, a former competitive runner from Sweden. Not surprisingly, she had no problems. In fact, instead of walking the peace march from Copenhagen to Paris two years ago, she ran it. She, too, refuses to divulge her shoemaker. "I got them free," she said.

Iceland's Gudrun, slender and toned, said that when she decided to attempt the march, "I walked one day with my 11-year old son 20 kilometers through Reykjavik to try it out. It was easy."

She wears a pair of gym shoes "one or two sizes too big, with good thick socks. I've had no problems." Except one, she adds with a smile: "One twisted ankle from dancing a peace dance with American peace workers outside Philadelphia."

Two and a half years ago, three Norwegian women conceived the notion of a peace march. They were appalled by a nuclear weapons build-up so extensive that if the bombs started to explode, "they might peel off the earth like an orange," said one of the original organizers, Eva Nordland. The march blossomed into a Scandinavian event that took place late that summer as dozens of women walked from Copenhagen to Paris over the course of six weeks. One of them, so devoted to the march, sold her apartment to buy a bus for the journey. Last summer, the women marched through Russian cities, starting at Leningrad, then going to Kalinin, Moscow, Smolensk and Minsk.

Two of the three initial founders are not marching this year--one is expecting a baby and another just had one. Nordland, a professor of education from the University of Oslo, is here on this march, along with her husband, Odd Nordland, a professor of social anthropology at the university.

There are more than 100 women marching and about a dozen men. Many are professionals and are devoted to educating the public--and in this case, the American government--to what they see as the dangers of nuclear weapons.

They are pro-nuclear freeze and, like many vocal European groups, are strongly opposed to the controversial deployment of Pershing II and cruise missiles in Europe, a sentiment they conveyed in an open letter to President Reagan and the American people.

"I don't want to be unilateral," said Host-Madsen, who decribes herself as a socialist. "I don't want to protest just in Moscow. I want to protest in the U.S. I haven't seen the U.S. making any peace propsoals. I don't call the zero-option plan a peace proposal."

"At first we would hear cries of 'Communists' or 'Nuke them,' " said Nordland about the comments from people passing in cars on this Atlantic Coast journey. "But a much larger group who are curious say, 'Don't we need nuclear weapons?' and that's wonderful. You can use that as a chance to talk."

Much of the reaction has been favorable, they said.

"People are waving and making the peace signs from cars," said Englander. "Most black people seem sympathetic."

They each paid their own air fare--$500 round-trip, Oslo to New York--and $200 to Peace March '83 for expenses here. The U.S. coordinator, Cornelia Dunn Clark, is the assistant director of the Unitarian Universalist U.N. office, and various Unitarian Universalist churches have provided lodging along the way.

Yesterday the group marched to the State Department and met with two officials. "We had an interesting and stimulating discussion about disarmament," said Jack Binns, director of northern European affairs. "I thought they were very serious. I wouldn't have wanted to march from New York to Washington in this weather."