ATHENS, Greece – Greece’s finance ministry Friday extended the deadline for holders of Greek bonds issued under foreign law or by state enterprises to agree to swap them with new securities worth less than half their original value.

The exchange will complete the biggest debt writedown in history, relieving the crisis-hit country of just over half its $271.5 billion debt held by banks, pension funds and other private investors.

The deal is intended to secure Greece’s long-term debt sustainability, bringing the amount owed to its creditors below 120 percent of gross domestic product by 2020, from nearly 170 percent.

It will also shift most of the country’s debt from private ownership into the hands of its bailout creditors — fellow eurozone countries and the International Monetary Fund.

Earlier this month, Athens traded government bonds worth $234.4 billion issued under domestic law for new ones, forcing investors to take a cut of more than half the face value of their bonds and accept more lenient repayment terms.

Friday’s finance ministry statement gave a new deadline of April 4 for owners of around $38.3 billion in bonds issued under foreign law or by state enterprises that are guaranteed by the state to accept the deal.

The ministry warned that holdouts who refused the deal would be forced to take the same payment as those who accepted it.

After years of mismanaging its state finances, Greece has been kept from bankruptcy since May 2010 by international rescue loans, agreed in exchange for harsh austerity measures meant to tame bloated budget deficits.

But the cutbacks have resulted in a deep recession, with the economy forecast to shrink for a fifth year in 2012.