The foreign teams often get fan support from Dallas-area compatriots, who add color and excitement to the games. Tahuichi, the world-renowned Bolivian youth team that has won the under-19 boys title for the past two years, plays its games against a background of swirling flags, beating drums and chants of ''Bolivia! Bolivia!'' from a score of devoted fans. ''We even had a call once from a group in Los Angeles,'' Griffith said. ''They said they were Maltese and they were coming to support the Maltese team. As it happens, we didn't have a Maltese team. All we had was a Maltese referee. And he didn't show up.''

The Dallas Cup scored an international breakthrough this year when, after years of polite nyets, teams from the Soviet Union suddenly agreed to attend. Three under-19 boys teams - from Estonia, Lithuania and the Ukraine - are playing in this week's tournament. Some Stay With Families

The boys from the Soviet Union, like the players from 20 other foreign teams, are staying with Dallas families.

''I'd really like all the teams to be with families,'' said Griffith, who traveled to 27 countries last year recruiting for the Dallas Cup, ''but clubs are now serious about winning here, and some prefer to have their players all together in a hotel.''

The Mapes family is host to two boys from Dynamo Kiev, and the foreign players have proved a surprise to 11-year-old Justin Mapes, who thought ''they'd be boring and ignore us and not want to learn what we do.''

''But Igor and Alek are really nice,'' he added. ''They're really funny.'' Ann Danford, who has been a host for overseas teams for eight years, said of two other players from Kiev, Yuri and Andre: ''You couldn't ask for two sweeter kids. They're tidy, they're polite - and they insist on washing their own uniforms.''

Denis O'Hagan is housing two 12-year-olds from Thailand. He admits to a communication problem that requires a lot of miming and gesticulating. ''We weren't sure what they would like to eat, but we're learning,'' he said. ''We hold up an egg, and they nod. We show them a can of Coke, and they smile. And they love popcorn. It's a real neat experience.''