Moscow took quick, drastic steps to ease investors and panic-stricken Russians who dumped their national currency in exchange for durable goods and dollars as the ruble lost a quarter of its value yesterday. President Boris Yeltsin promptly sacked Finance Minister Sergei Dubinin and moved to fire the Central Bank chairman, Viktor Gerashchenko. He made it clear that he suspected foul play, calling the ruble's plunge an act "of sabotage or the manifestation of a policy of extreme irresponsibility and slovenliness by the special groups of people . . ."