As the mother of three teen-agers, Rita Russian of Needham, Mass., had no illusions about hosting a 17-year-old foreign-exchange student. She and her husband, Hrant, were ready for the challenges but also expected the experience to be enriching and fun.
''Teen-agers are so receptive at this age. They are willing to change and they do,'' says Mrs. Russian.
Now, as their Finnish exchange student, Tuija, prepares to leave, Mrs. Russian looks back over the year. ''It has been crazy and nerve-racking at times , but we've come to love her,'' she says. ''I think the children will look back on it as a special year.''
Traditionally, student-exchange programs have appealed to families with teen-agers. Now they are beginning to reach a wider audience. Parents with small children, single parents with children, retirees, and even a few single people are welcoming foreign students into their homes.
''We are dealing with a more diversified group in terms of family composition ,'' says Ase Hansen, United States hosting coordinator for the American Field Service International (AFS). ''The whole notion of family has changed drastically in America, and we as an organization are finally catching up with it.''
As their numbers proliferate, student-exchange organizations are facing increased competition from each other and from governments and travel agencies offering comparable experiences. Recruiting host families is sometimes difficult , particularly in regions with depressed economies.
In the past two years some student-exchange programs have benefited from the President's International Youth Exchange Initiative, announced in May 1982. The program promotes cross-cultural ties and provides funding for student-exchange organizations.
''With the push for student exchange, people are becoming more aware of programs,'' says Karen Rudnick, associate regional director of Youth for Understanding (YFU) in Boston - one of the largest international exchange groups. ''Unfortunately, there are still a lot of bad programs. People are beginning to shop around and choosing programs that have a good reputation.''
Mrs. Rudnick and her husband have hosted four exchange students over the past eight years, beginning when their own daughters were ages 1, 3, and 5. They have hosted students from Mexico, Sweden, and France and are currently hosting a teen-ager from Denmark.
''For my kids it's been fabulous,'' she says. ''Our French student played the harp - she was really outstanding. It influenced my oldest daughter to play the piano. Our Danish student is teaching her to speak Danish, and they can communicate with each other (in Danish) at the dinner table.''
Youth for Understanding and other exchange groups emphasize the importance of including foreign students in everyday family routines and activities.
''The ideal situation is a family that can treat these students like one of their own kids,'' says Mrs. Rudnick. ''Our Danish student said she felt she was really part of the family when I walked up to her room with a garbage bag and shovel and told her to clean up her room.''
Don and Anne Livingston of Lexington, Mass., give their foreign-exchange students extra support and attention when they first arrive.
''They do seem to have difficulty making friends right away, and we try to do things to take their minds off their loneliness,'' says Mrs. Livingston. ''We have found they are generally more mature than American teen-agers their own age.''
The Livingstons began hosting students through YFU when the youngest of their three children was in college. They have hosted four students so far: one from Colombia, one from Australia, and two from Japan. They have applied for another student this year.
Mr. Livingston enjoys seeing the student's progress over the school year. ''It's a challenge to help them learn to communicate with ourselves and others, '' he says. ''It's gratifying to see them pick up the language so well in less than a year.''
Foreign exchange students can also make a difference beyond their immediate host family.
Neal Grove, director of research for AFS, describes a particularly successful experience he uncovered during an in-depth study of 15 American host families. In this case, a young man from Chile was an enjoyable addition to his host family and became a favorite in their small town in central Pennsylvania.
In the last week before the student's departure, Mr. Grove wrote in a preliminary report, the student was ''honored and feted not only by his host family and circle of friends, but also by virtually everyone in the neighborhood and even by people in the wider community.''
In other cases, conflicts arise that result in moving the student to another host family during the course of the year.
At YFU, Karen Rudnick says, ''We move a lot of students - about 20 to 25 percent - to another family. If you have a student moved, you haven't failed. Sometimes a student will come and they are very different from their application. It's just not a good match.''
Some host families that encounter difficulties with their students are still able to achieve a satisfying overall experience.
''It's not easy to be responsible for someone else's child,'' says Marilyn Kassirer. She and her husband, Stanley Wayne, have had students from Germany, Brazil, and Denmark in their Brookline, Mass., home. They have a five-year-old son of their own, and Mr. Wayne has two grown children from a previous marriage.
''It's always a challenge to deal with a teen-ager. But your perspective is different than with a child of your own. One of our students was having some difficulties, and we were able to sit down and talk things through. At home (the issue) might have resulted in an all-out emotional battle.''
For this professional couple, hosting students has brought more community contact.
''We became involved in high school activities we wouldn't have otherwise and got to meet a lot of the older neighborhood kids. That was a nice bonus,'' says Ms. Kassirer. They also keep in touch with the students they have hosted and have met two of the students' three families. ''It's a wonderful experience,'' she says. ''You don't only gain the student, you gain their whole family.''