Seiji Ozawa is under contract as music director of the Vienna State Opera through 2007, so it isn’t surprising that VSO officials are being coy about rumors that they are actively pursuing Franz Welser-Möst to replace him. Welser-Möst, the young music director of the Cleveland Orchestra, was first mentioned as an object of Viennese desire more than a year ago, but the talk of his wooing has revved up since he stepped in for an ailing Christian Thielemann last month, and led a well-received production of Wagner’s Tristan & Isolde. Complicating the rumors is the fact that Welser-Möst’s contract in Cleveland was recently extended through 2012.