PARIS, Nov 12 (Reuters) - Policymakers should consider ways of shifting from a dollar-centric global monetary system to one with a wider range of reserve assets and some form of insurance that would reduce reserve accumulation, IMF economists say.

The worst economic downturn in 70 years has revived concerns over a monetary "non-system" where the weaknesses have amplified as emerging economies built up reserves to self-insure against capital account crises in recent years, the economists say.

The economists laid out their thoughts in a paper that does not commit the International Monetary Fund as an institution and essentially amounts to a review of options governments may want to consider as they seek to deliver on G20 pledges to push for a more balanced economic system.

To ease reserve demand, policymakers could explore promoting alternatives ranging from third-party insurance to a system where countries could borrow from global or regional reserve pools through a lender of last resort.

The latter was a role the IMF could play but only if it had far greater resources, said the paper, which noted that academic estimates of the necessary resources were anything from $1 trillion to limitless.

"In addition to the IMF, other insurance arrangements, such as regional pools and bilateral swaps, would be useful complements, although with more limited scale, scope for risk sharing, and surveillance arrangements," says the paper.

Many of the ideas aimed at attenuating demand for reserves would only partially address the problem, however, and there was still a need to consider alternative reserve currency systems in place of the currency dollar-based one, it says.

Alternatives ranged from a system of multiple or competing reserve currencies with no dominant one, a system based on the IMF's SDR unit of account that pools the main reserve currencies or a totally new global currency that trades alongside others.

A multi-currency system could emerge with time even if there were few precedents and the most likely contenders were the euro in the first instance and later on the yen and yuan, the paper says.