ATHENS — Prime Minister Lucas Papademos urged Greeks on Saturday night to accept a tough new austerity package sought by its lenders. The alternative, he said, is certain bankruptcy.

“We are a breath away from ground zero,” Mr. Papademos said in a televised address to the nation ahead of a crucial parliamentary vote on a new debt deal scheduled to take place on Sunday night.

The austerity program — which foresees cuts to private sector wages and private sector layoffs — is tough but will “restore the fiscal stability and global competitiveness of the economy which will return to growth, probably in the second half of 2013,” the premier said, adding that the deal would safeguard the country’s future in the euro zone and encourages skeptical investors to return to Greece.

Greece’s so-called troika of foreign lenders — the European Commission, European Central Bank and International Monetary Fund — has demanded the austerity measures in exchange for about $170 billion in bailout money that Greece needs in order to avert default. The troika has also made passage of the measures a condition for sealing a deal in which private creditors will take voluntary losses of up to 70 percent of Greek debt.

Mr. Papademos said that those who argue that bankruptcy would be preferable to additional austerity are “woefully mistaken.”

“A disorderly default would throw the country into a disastrous ordeal,” he said. “It would create conditions of uncontrollable economic chaos and a social explosion.”

Greece’s cabinet approved the package after five hours of debate on Friday and sent it on to Parliament, where it is also expected to pass. While several members of Parliament from the coalition parties — the Socialists and the center-right New Democracy — have indicated that they will vote against the deal, the dissent is far from the level needed to prevent it from passing. Still at least 10 lawmakers from New Democracy have said they will vote no and the number of dissenters among the Socialists is believed to be close to 20 though only a handful have expressed their intentions. Three members of Parliament have resigned from the Socialist party.

Outside Parliament on Saturday, union leaders held a demonstration that attracted about 3,500 protesters, according to the police, who said there had been no arrests and could not confirm media reports of two minor injuries to demonstrators. Local media reported that at least 4,000 officers were on duty. Another protest was expected on Sunday.

Hours before prime minister spoke, the leaders of the two parties remaining in Greece’s shaky coalition government urged lawmakers to approve a debt deal.

Antonis Samaras, the conservative leader of New Democracy who is likely to be the next prime minister of Greece, said that elections should also be called immediately after the completion of a debt-swap deal being negotiated between the government and private creditors. And in a bid to discourage would-be dissenters, Mr. Samaras has warned members that anyone refusing to back the measures would not be a candidate in the coming elections.

George Papandreou, the former prime minister and leader of the Socialist party, which has seen its support plummet, appealed to his deputies to put party interests aside for the good of the nation. He compared Greece to a parched traveler. “We’ve gone too far to turn back now,” he said. “We have reached the source. The country must drink water.”

In his speech, Mr. Papademos appealed to Greeks, who have already faced two years of austerity in the form of wage cuts and tax increases, to be patient.

“We know that people’s endurance has reached the limit,” he said, adding that the sacrifices have started to bear fruit. The primary budget deficit has been reduced to 5 billion euros from 24 billion euros in two years, he said, noting that the country had regained a third of the competitiveness it had lost in the last decade.

Although the austerity program foresees tough cuts, Mr. Papademos said, it includes reforms that should have been taken years ago to bolster the Greek economy.

The current recession, now in its fifth year, is due to “a constantly increasing borrowing,” he said. ”When the borrowed money finished, the state could no longer finance its expenses, consumption fell and economic activity shrank.”

Greeks must now change their ways, he said. “We can no longer produce more than we consume,” he said.

In a nod toward growing public anger with demands by foreign creditor states for a tougher approach to Greeks, Mr. Papademos noted that the country was getting something in return. “We must not forget that Greece today is receiving the biggest package of rescue funding ever given and with extremely favorable terms. This reflects our partners’ will to keep us in the euro. This is why they are pressurizing us, so we can make use of this support.”

Bankruptcy and an exit from the euro zone would be “the greatest defeat” for a proud and open? nation, the Greek premier said.

“It would be a great injustice? of history if the country where European civilization was born, which in the past 65 years has? experienced a civil war and a dictatorship, and yet prospered, built a democracy, institutions and values, reached? the point of going bankrupt and finding itself, from yet another error, in national isolation and despair”