International banks and insurers will thrash out improvements to a plan for the private sector to contribute to Greece's bailout effort at a meeting in Paris on Wednesday, in a bid to prevent the proposal coming unstuck.

The Institute of International Finance (IIF) lobby group said it will chair the meeting of private sector creditors and officials.

The IIF Friday said banks supported proposals to aid Greece and were considering a small number of options. Creditors are now trying to hammer out details.

A meeting involving some banks was held in Paris Tuesday in an informal discussion to resolve issues, people familiar with the matter said.

French banks, major holders of Greek sovereign debt, have proposed voluntarily renewing Greek bonds when they fall due, but on different terms, which could trigger a default.

Getting clarity on the accounting treatment of France's plan remains a key issue to getting momentum, sources said.

Politicians and bankers had expressed confidence last week that the French proposal would not trigger a default, but rating agency Standard & Poor's Monday said it would involve losses to debt holders, most likely earning Greece a selective default rating.

Under France's plan bondholders would reinvest at least 70 percent of the proceeds from bonds maturing between now and the end of 2014 in new 30-year Greek debt.

The IIF, which represents insurers and other financial firms as well as banks including BNP Paribas, Deutsche Bank, HSBC and Societe Generale, is playing an informal role co-ordinating international banks to reach consensus about private-sector involvement in a bailout of debt-ridden Greece.

Wednesday's meeting will be chaired by Charles Dallara, IIF managing director. It is one of a series of meetings the IIF is co-ordinating, running in tandem with technical discussions held since an IIF meeting in Rome a week ago.

(Reporting by Alex Chambers, IFR Markets; Additional reporting by Steve Slater in London and Jean-Baptiste Vey in Paris; Editing by Hans-Juergen Peters and David Hulmes)