BRUSSELS – Europe’s biggest banks must raise billions of euros in capital to better withstand market turmoil, the European Commission proposed Wednesday as it embarked on a major push to contain the continent’s escalating debt troubles and avert a second recession.

The fear gripping the financial sector is that banks may soon have to take big losses on bonds they own from governments with shaky finances, like Greece. That uncertainty is stifling lending — both between banks and to the wider economy — and threatening to kill off a halting recovery in the 17-nation eurozone and much of the rest of the world.

The commission, the European Union’s executive body, believes that boosting confidence in Europe’s financial sector is a crucial step that will allow the continent’s leaders to tackle Greece’s massive debts and stop the debt crisis from spinning out of control. The commission also is trying hard to protect large, troubled economies like Italy and Spain, which are too big to be bailed out, from being dragged into the debt crisis.

Wednesday’s proposals foresee that key lenders in Europe will have to implement new international rules on bank capital much earlier than 2019, as was initially planned.

The proposals are part of a broader plan to tackle the currency union’s debt troubles, which have dragged on for close to two years. The EU’s executive body hopes the leaders of the 27-nation bloc will embrace its suggestions at a crucial Oct. 23 summit that officials believe may be their last chance to solve the debt crisis before it really explodes.