MANCHESTER, Maine (AP) _ Schoolmates of the late Samantha Smith said Monday that their trip to the Soviet Union was a step toward their friend's goal of world peace.

Jane Smith, mother of the amateur ambassador, stayed in Moscow hoping to complete arrangements for a reciprocal visit to the United States by Soviet youngsters. She planned to return home Wednesday.

The trip was ''exhausting but very productive,'' said William Preble, a Maranacook Community School teacher and chaperone who returned with the 20 pupils Sunday night.

Preble said the teen-agers made friends easily with their Soviet peers and that even a few fleeting romances developed during the 12-day trip, which took the Americans to Moscow, Leningrad and a youth camp on the Black Sea.

''The measure of success was, at every stop, they didn't want to leave,'' he said.

Samantha, who died at age 13 in a plane crash with her father and six other people in August, had toured the Soviet Union in 1983 at the invitation of Yuri Andropov, then-leader of the Soviet Union. She had written to Andropov expressing her hope for peace.

The youngsters said Monday that the friendships they made were a step toward achieving world peace.

Mark Bates of Readfield said he believed exchange visits between the two superpowers would help lessen the chances of war.

If enough exchanges were made, leaders of the two nations would ''be less apt to start a war because there would be so many friendships in the two countries, no one would want a war.''

''I think we were alike in most ways,'' Sarah Warren of Manchester said, ''except that we spoke (different) languages.''

Preble said Soviet officials were receptive to the idea of sending Soviet youngsters to the United States next year as guests of the school's Project SAME, or the Samantha Smith Soviet-American Memorial Exchange.

Tentative plans call for the Soviet students to visit Washington, Boston and a children's camp in Union, Preble said.

The trip was sponsored by the Samantha Smith Foundation. Travel costs were paid by Turner Broadcasting Systems, which is co-sponsoring the inaugural Goodwill Games with the Soviets, and the Soviet government picked up the tab for food, lodging and travel in the Soviet Union, Preble said. Parents also raised money to cover other costs, he said.