Dashed Dreams: Visas Invalid, Airline Workers Told
United States immigration officials inform 28 Delta airlines flight attendants from Poland that their work visas were issued by mistake, and that they and their families must leave country within two weeks--even though they have no jobs back in Poland, and in many cases no homes; Delta execs say that they are sorry to lose their workers, but that they have exhausted their efforts to appeal decision; photo (M)