Athens, Greece ? Greece’s private creditors agreed Friday to take cents on the euro in the biggest debt writedown in history, paving the way for an enormous second bailout for the country to keep Europe’s economy from being dragged further into chaos.

Greece would have risked defaulting on its debt in two weeks without the agreement, sparking turmoil in the markets and sending shock waves through the other 16 countries that use the euro.

Prime Minister Lucas Papademos called the deal — which shaves some $138 billion off Greece’s $487 billion debt load — an important “historic success” in a televised address to the nation Friday night. “For the first time, Greece is not adding but taking debt off the backs of its citizens.”

The country said 83.5 percent of private investors holding its government debt had agreed to a bond swap, taking a cut of more than half the face value of their investments as well as accepting softer repayment terms for Greece.

The swap aiming to turn around the country’s debt-ridden economy was a key condition to secure a $172 billion rescue package from other eurozone countries and the International Monetary Fund.

The managing director of the Institute of International Finance, which negotiated the deal with Greece for large investors, called the bond swap “the largest ever” debt restructuring.

“This has been painful and the pain is not over yet. But I now can see light at the end of the tunnel for the Greek economy,” Charles Dallara told Greece’s Mega television. He estimated Greece could return to the markets “within a few years.” If recovery continues, “I think the risk for Greece and the risk on the eurozone will be very manageable,” he said.

Of the investors holding the $234 billion in bonds governed by Greek law, 85.8 percent joined. The deadline for those owning foreign-law bonds was extended to March 23.

Creditors holding Greek-law bonds who refused to sign up will be forced into the deal.

The decision to force losses on some bondholders means that the debt relief will trigger payouts of so-called credit default swaps, a type of insurance on bonds. The International Swaps and Derivatives Association, the private organization that rules on such cases, said its committee ruled that a “restructuring credit event” occurred.

When the debt relief plan was first announced last year, eurozone leaders and the European Central Bank worked hard to avoid a credit event because they feared the payout of credit default swaps could destabilize big financial institutions that sold them.

But since then, that prospect has started to look less threatening. The ISDA said that if triggered, overall payouts will be significantly below the $3.2 billion in net outstanding credit default swap contracts linked to Greece. The exact level of payouts will be determined on March 19.

The Fitch ratings agency downgraded Greece to “restricted default” over the bond swap — a move that had been expected. Fitch was the third agency to downgrade Greece into default, after Moody’s and Standard & Poor’s. The agencies are expected to raise the country’s credit rating after the completion of the swap.