* UN proposes carbon, billionaires, currency taxes
* UN says more money needed for aid, global challenges
* UN has no authority or mechanism to enforce taxes
UNITED NATIONS, July 5 (Reuters) - The United Nations on Thursday urged countries to impose international taxes to raise more than $400 billion a year, such as a carbon tax, a currency transaction tax and a billionaires tax, to offset cutbacks in aid by many countries amid global economic turmoil.
The U.N. World Economic and Social Survey found the needs of developing countries were not being met, more money was needed to fight challenges like climate change and new taxes would help "donor countries overcome their record of broken promises."
The United Nations has no authority or mechanisms to enforce an international tax and can only urge its 193 members to do so. The world body plays a marginal role in economic issues, which is the realm of the World Bank and International Monetary Fund.
"Donor countries have fallen well short of their aid commitments and development assistance declined last year because of budget cuts, increasing the shortfall to $167 billion," the survey's author, Rob Vos, said in a statement.
"We are suggesting various ways to tap resources through international mechanisms, such as coordinated taxes on carbon emissions, air traffic, and financial and currency transactions," he said.
Some United Nations officials have made various global economic proposals such as replacing the U.S. dollar as the world's currency with IMF Special Drawing Rights, an idea that a number of countries have been pushing.
One suggestion made in The World Economic and Social Survey was that regular allocations of IMF Special Drawing Rights and use of idle Special Drawing Rights could produce about $100 billion annually to buy long-term assets that would then be used as development finance.
The survey also said a $25 per tonne tax on carbon emissions in developed countries - collected by national authorities but allocated for international causes - could raise an estimated $250 billion a year.
Another $40 billion a year could come from a 0.005 percent transaction tax on the four main currencies, the U.S. dollar, euro, yen and the British pound. A tax of 1 percent on billionaires could also be explored, the survey said.
"Realizing the potential of these mechanisms will require international agreement and corresponding political will, both to tap sources as well as to ensure allocation of revenues for development," Vos said.