The idea is to identify who is keeping their currency artificially low to boost exports, Mantega said, lending support to eventual actions against illegal subsidies at the World Trade Organization.
"The IMF would have to come up with a method to measure which currencies reflect the structural situation of their countries, which are floating currencies, and which ones are forcing their hand," Mantega told O Globo newspaper in an interview.
The next step would be to make a deal to reduce such intervention, and if that didn't happen the manipulation could eventually be considered a commercial subsidy, Mantega said.
"In fact, the WTO considers currency manipulation to be a commercial subsidy that has to be avoided and could result in sanctions", he said.
Many countries are already taking measures to devalue their currencies, Mantega said, highlighting Japan and South Korea. An IMF index would bring greater transparency, he added.
Brazilian officials have been at the forefront of a global battle on currency intervention, criticizing the monetary policy of advanced countries while taking measures at home to halt the rise of the real.
Over the past month, Brazil tripled a tax on foreign investment in local bonds, closed a series of loopholes to make the tax more effective and raised a tax on the collateral investors must put down to trade in the futures market.
The measures have helped to somewhat contain a rise in the real, but it is up more than 5 percent against the dollar since late June.
Brazilian officials worry a failure to achieve a global solution to the currency imbalances problems will lead to more unilateral restrictions on capital inflows and eventually to commercial restrictions.
"We risk having a trade war, and that's the worry," Mantega said earlier this month. (Reuters)
