SYDNEY (Reuters) -A trade war sparked by U.S. President Donald Trump's tariffs may drive up global inflation, stoke market volatility and slow economic growth, the CEOs of two top Australian banks said on Tuesday, but added Australia was insulated from the disruption. The heads of No. 1 retail lender Commonwealth Bank of Australia and No. 1 business lender National Australia Bank told a conference the new U.S. administration's protectionist policies would likely strain the global economy in the medium term with higher costs and lack of certainty. But Australia's roughly $15 billion a year in exports to the U.S. was small compared to its overall export trade, so the country was better placed than Canada, which sells 85% of its exports to the U.S., the financial leaders added.