MELBOURNE -- Standard&Poor's CreditWire 8/21/96 -- Standard&Poor's today has affirmed its double-`A' long-term rating on the Commonwealth of Australia, and has revised the foreign currency rating outlook to positive from stable. At the same time, the triple-`A' long-term rating on Australian dollar denominated debt and the `A-1'-plus short-term rating are affirmed. The outlook change reflects the substantial fiscal tightening implied by the Commonwealth government's budget statement released yesterday and Standard&Poor's expectation that Australia's net public external debt burden could decline markedly if this fiscal stance is maintained medium term. Both foreign currency and local currency ratings balance Australia's diverse and increasingly competitive economy and narrowing fiscal imbalances with a high net public external debt