Peace marchers, 220 strong, have gathered in Loudoun County this week to prepare for a 450-mile trek across Russia in the name of nuclear disarmament.

On Sunday they are to leave Dulles International Airport for Leningrad, where they will be joined by 200 Soviet counterparts for a march to Moscow, sponsored by the Soviet Peace Committee. Along the way, they hope to plant the seeds of an end to the Soviet-American arms race, they say.

About 79 of the American marchers are veterans of the 3,700-mile Great Peace March across the United States last year, out of which came the idea for the American-Soviet walk. Coordinators say this march is better organized and better funded. Each marcher was required to provide $2,500 toward the event.

The weeklong orientation is being held at Glaydin School, a facility for troubled youngsters near Lucketts. If arrivals are not sure they are in the right place, a look at the bumper stickers in the parking lot will reassure them.

"Arms Are for Hugging." "Be All You Can Be. Work for Peace." "Think Globally -- Act Locally."

The marchers include business people, teachers, diesel mechanics, artists, sales clerks, engineers, musicians, construction workers and doctors. They come from all walks of life, said Allan Affeldt, president of the Peace Walk, the organizational arm, and they represent all parts of the political spectrum.

"Peace isn't an idea that belongs to one political party," he said, citing endorsements the group has garnered from senators and representatives from the two sides of the aisle. "Or even just to one country. The Soviets want it, too."

At the first orientation meeting Monday night, marchers sat on the floor and outside on the wooden porch listening to organizers tell them what to expect -- and not to expect -- during their hike across Russia.

"There will be lots of food," Affeldt told them, "and we'll be able to take showers most nights. The Soviets are eager to make sure we're happy and comfortable. But they have a different idea of camping than we do."

The colorful domed tents the marchers will share will not be pitched in fields and deserts and other natural sites as they were during the 1986 march. The Soviets have made arrangements at hotels all along the route, where marchers will be invited in off the road.

Hotel parking lots will be available for those who choose to rough it, Affeldt said, although some Russian communities will make some campsites available.

"I intend to walk as much as I can and stay out of hotels as much as I can," said marcher Mary Edwards, grandmother of seven. "And I want a Soviet tent mate." Edwards said she is trying to keep an open mind about the Soviet people. "I expect I'll find whatever I'm looking for," she said. "I'm going there to experience them."

This week, marchers are learning how to handle confrontation and conflict, how to avoid cliches and stereotypes, and how to "educate the Russians they meet that the average American wants peace."

Affeldt said Soviet officials have promised the group "freedom of expression" so that marchers can discuss Afghanistan, Nicaragua and Soviet Jewry, as well as disarmament, with the Russians they meet. In addition, reporters and photographers on the trip will be allowed to write about and photograph "anything they want," he said.

Five years ago, none of this would have been possible. He credited the glasnost (openness) policy of Soviet leader Mikhail Gorbachev for the change.

"When we began to organize this march in February, they told us it couldn't be done in four months," he said, "so of course that's why we decided to do it. Well, 'they' also say we can't get an arms agreement. But we can -- if enough of us want it."