Diplomats See Kremlin-Crasher

West German officials had their first talk today with the teen-ager who flew a light plane to Red Square through 400 miles of Soviet air defenses, and they said he appeared to be reacting calmly to his stay in prison.

An embassy official who spoke to reporters after the meeting at Lefortovo prison gave few other details of 19-year-old Mathias Rust’s condition or of what Soviet authorities plan to do with him. Soviet law allows 10 days for authorities to tell Rust what points they are investigating and two months, which may be extended to nine, to complete the investigation.