BERLIN – The 17-nation eurozone is set to shore up its bailout fund to contain the debt turmoil that threatens to engulf more countries across Europe, and German lawmakers said Monday the plan could boost the fund’s lending capacity to more than 1 trillion euros.

A document obtained by The Associated Press shows the currency zone wants to boost the 440 billion euro bailout fund by offering sovereign bond buyers insurance against possible losses and by attracting capital from private investors and sovereign wealth funds.

Eurozone governments hope that the enhanced European Financial Stability Fund, or EFSF, will be able to protect countries such as Italy and Spain from being engulfed in the debt crisis. To do that, however, it needs to be bigger or see its lending powers magnified.

Leading German opposition lawmakers, who were briefed earlier Monday by Chancellor Angela Merkel on the plan, said the fund’s lending capacity will be boosted “beyond 1 trillion” euros.

But the draft document by the eurozone working group — which Germany’s government was sharing with key lawmakers Monday — did not provide a headline figure for the bailout fund, stressing “a more precise number on the extent of leverage can only be determined after contacts with potential investors” and rating agencies.

Because of the move’s significance, members of Merkel’s party proposed that the change receive full parliamentary approval on Wednesday — although it would have been enough for the parliament’s budget committee to approve the plan.

The changes look likely to pass by a wide margin in Germany’s parliament.

Lawmakers will vote only hours before an EU summit in Brussels that is set to adopt the new rules for the EFSF.

But any assistance from the fund for member states would have tough strings attached and the “appropriate monitoring and surveillance procedures,” the document said.

Greece, for example, must implement harsh austerity measures in return for last year’s 110 billion euro bailout.

Beefing up the EFSF is one part of a three-pronged eurozone plan to solve the crisis.

The other two parts are reducing Greece’s debt burden so the country eventually can stand on its own and forcing banks to raise more money so they can take losses on the Greek debt and ride out the financial storm that will entail.

Greece’s private bondholders agreed in July to accept losses of 21 percent on their holdings, and getting them to take deeper losses to lighten the country’s debt load is proving particularly difficult.

Experts agree that Greece needs to write off more of its debt — German officials have said up to 50 or 60 percent — if it is ever to get out of its debt hole.

But many say such a deal with private creditors needs to be voluntary. Imposing sharp losses against the banks through a so-called haircut could trigger massive bond insurance payments that could cause panic on financial markets.

Charles Dallara, managing director of a global banking lobby group currently negotiating a wider Greek debt reduction with eurozone officials in Brussels, cautioned that “there are limits to what could be considered as voluntary.”

He insisted that any approach not based on cooperative discussions but unilateral actions would be tantamount to a Greek default, isolating the country for years from capital markets.

“It would also likely have severe contagion effects, which would cost the European and the world economy dearly in terms of employment and growth,” Dallara said in a statement.

The European Central Bank, meanwhile, has been taking on the role of firefighter by buying the bonds of financially weakened governments on the open market.