Ahead of lawmakers' confidence vote on his new crisis cabinet, Greek Prime Minister George Papandreou Sunday defended the austerity package and called for a referendum in September to change the country's constitution.

Speaking at the onset of a three-day debate in parliament, Papandreou urged Greeks to support the unpopular package in order to overcome the country's worsening debt crisis.

"Our top priority at the moment is to conclude the negotiations to secure further support from our European counterparts and the International Monetary Fund to counter the debt crisis," said the prime minister.

Acknowledging chronic shortfalls in the political system of the debt-ridden country, which have contributed to the current crisis and fuelled people's discontent, he announced his intention to seek a constitutional revision that could boost transparency, address corruption and improve the state's function.

Papandreou told parliament the proposed fall referendum would remove those unfit for key government posts and asked for support in the confidence vote to his newly appointed cabinet on Tuesday.

He warned again of the "sudden death of uncontrolled default" without the EU and IMF aid, calling on opposition parties for national consensus that would strengthen the country's stance in ongoing negotiations.

But Antonis Samaras, head of main opposition New Democracy Party, took the floor after Papandreou and rejected both calls.

One in two Greeks objects to the austerity package of spending cuts, tax hikes and privatization programs set to be voted on June 28, according to a new poll conducted for a Greek newspaper.

Greek labor unions and non-party affiliated demonstrators are scheduled to stage another anti-austerity protest in front of parliament later on Sunday.

Papandreou and Evangelos Venizelos, Greek new finance minister who was sworn in on Friday during the cabinet reshuffle, promised that the new government would try harder to ease the burden of the most vulnerable groups hit by the crisis. This has been the main request of thousands of protesters on the streets over the past weeks.

"I respect protesting citizens. There is always room for simple, direct, practical solutions to problems," Venizelos said in a statement to the Greek Sunday newspaper "To Vima."

Venizelos met with eurozone finance ministers in Luxemburg on Sunday over the release of further aid to Greece on the condition of new austerity measures, while Papandreou is due to hold meetings with Eurogroup President Jean-Claude Juncker and European Commission head Jose Manuel Barroso on Monday on the same issue.