BRUSSELS (AFP) - Eurozone leaders want to ramp up the firepower of their 440-billion-euro ($612 billion) bailout fund, the European Financial Stability Facility, at a summit on Wednesday. But they want to do that without increasing the guarantees provided by the 17 eurozone states, which would be politically untenable for eurozone paymaster Germany and other nations tired of bailing out weaker ones. After Greece was bailed out by the EU and IMF in May 2010, the EFSF was created the same month to protect other weak eurozone members. The fund was subsequently used to rescue Ireland and Portugal, but it would likely be insufficient to save bigger nations in trouble, the eurozone's third and fourth biggest economies, Italy and Spain. Two models, which could be combined, are under negotiation to "leverage" the capacity of the EFSF to more than one trillion euros: The EFSF could guarantee between 10 and 20 percent of the debt issued by fragile states such as Italy or Spain, which are paying high interest rates to borrow on the bond market. The goal is to maintain the confidence of investors and convince them to demand lower interest rates. The risk, however, is that insuring new debt issued by states would undermine the value of older bonds already in circulation, which would be bad news for investors holding them. This, in turn, could aggravate a country's debt, causing the opposite effect that was originally intended. A special fund could be created to attract deep-pocketed private and public investors, including countries outside the eurozone such as China, which is ready to participate, according to senior EU diplomats. The fund could be a "special purpose investment vehicle" linked to the EFSF, with investors voluntarily providing capital and/or guarantees. This would allow the EFSF to raise even more money on the bond market that would then be used to provide aid to distressed eurozone states by buying debt or recapitalising banks. Another option would be to link such a special fund to the IMF instead of the EFSF.