Preserving Two Chapters Of America's Songbook
John McGlinn, American conductor and music historian, is at work in London recording all shows and songs of Jerome Kern and Victor Herbert, undertaking supported by David Packard's Packard Humanities Institute; first discs in project, which should take 15 years to complete, are expected in 2002; Packard says it is cheaper to record in London, but McGlinn says real attraction is working with London Sinfonietta, Britain's premier contemporary-music ensemble; photo (M)
