Plot: with Leonard Bernstein conducting his Songfest 'I love the Proms' declared Leonard Bernstein, after his Prom debut last September with the Vienna Philharmonic - 'the audience is incredible, the atmosphere unique. ' Tonight Bernstein, who will be 70 next month, returns to the Proms conducting an international youth orchestra from the Schleswig-Holstein Music Festival in Germany, which he has been training for the past two years