Sir Simon Rattle saved the Boston Symphony's day at Thursdays regular subscription concert with a fine performance of the least interesting program of the season. Although skillfully conducted and performed, a Suite from Les Indes galantes (Love In Exotic Places) by Baroque composer Jean-Phillipe Rameau probably pleased only a minority of patrons tonight. About a dozen episodes from a popular light ballet of the period, the suite sounded to this listenner like elevator music before its time. Pleasant music composed for a partiuclar stage purpose, this material was composed to take the serious edge off of tragic themes usually presented at the French court in the late 17th century. Although it has none of the substance of Bach it also reflects a less serious purpose. Its attitude would have probably been better served with HIP instrumentation. Fortunatly the second portion of the concert saved the total program from being a dead bore. Rattle conducted the competently played for Beethoven Symphony #3 Eroica. This traditional repertory was saved from pot boiler status in this instance by a vigorously and imaginatively conducted performance of high calibre. In typical fashion, orchestra members rose to greet a guest conductor with their best playing. Ensemble performances were outstanding especially from the horns. Each movement and subsection was deliniated by tempi and instrumental treatment of continuing variety, dynamics and interest. Ah, ha! Victory snatched from the jaws of nearly certain defeat. Thanks, Sir Simon. Good show BSO instrumentalists! Bernard Gregoire Hingham, MA