Greece's socialists were set on Sunday to choose Finance Minister Evangelos Venizelos as their new leader in a bid to avert a disaster in upcoming elections after two years in power marked by austerity pain.

A French-educated law professor from the northern metropolis of Thessaloniki, Venizelos stands unopposed to take over the historic PASOK party which has ruled Greece for a combined two decades since democracy was restored in 1974 after a seven-year army dictatorship.

The 55-year-old told reporters last week that the election provided a good opportunity to energize the party ahead of legislative elections which are expected to take place in upcoming months.

"It will be a useful opportunity to rally the party, to mobilize and activate its reflexes,» he said.

Venizelos is hoping to capitalize on a record deal with private investors last week to erase more than 100 billion euros ($130 billion) of near and midterm debt to give Greece time to enact additional reforms needed for future loans.

But the International Monetary Fund reminded Athens on Friday that the pressure remains very much in place.

Greece has «little if any margin» for slippage on reforms under its new bailout program, according to IMF documentation for its loan to Athens.

The International Monetary Fund, which decided a new 28 billion euro loan for Greece on Thursday said Greece could reach its debt reduction targets if it adheres to the tough austerity measures -- including slashing minimum wages, trimming pensions and cutting 15,000 public jobs this year.

But if implementation moves too slowly or falls short, or if the economy does not respond to reforms as fast as expected, «a deeper recession and a much higher debt trajectory would be the likely result."

"Political risks linked to the electoral calendar create additional uncertainty about policy implementation,» the IMF added.

Venizelos insists that his goal is to win the next legislative election, which has not been officially announced but is expected in late April or early May.

"The goal can only be victory,» the bullish minister said last week. «We have a crisis in progress ahead of us, one that we must manage."

Around 390,000 card-carrying party members and millions of supporters have been called to participate in Sunday's nationwide procedure which will give an early indication of Venizelos' chances of turning around the party.

After two years in power before a coalition government was formed with the conservative New Democracy in November 2011, PASOK has been identified with an unpopular EU-IMF economic rescue plan and faces the lowest ratings in its 37-year history.

Appointed to the finance ministry in June, one of Venizelos' first acts was to push through an austerity law worth 28 billion euros ($37 billion), including 50 billion euros in privatization measures, in the teeth of violent street protests.

The party's outgoing leader George Papandreou, son of PASOK founder Andreas Papandreou, was forced to step down as prime minister a few months later to avert a backbencher revolt in parliament.

A poll in Kathimerini daily on Friday, which incorporated a large absentee expectation of 25.5 percent, put PASOK back in fifth place with 11 percent, far behind the conservatives who were given a 14-point lead.

The poll gives the new PASOK leader an approval rate of only 30 percent.

Greece's current coalition government, headed by former European Central Bank deputy chief Lucas Papademos, must still ratify in parliament a new eurozone bailout worth 130 billion euros designed to save Athens from default.

And the next government must pursue the unpopular economic overhaul on top of past tax hikes and wage and salary cuts that have plunged Greece into the worst recession in decades, with more than a million people officially out of work.

A gifted orator, Venizelos had previously campaigned to take over the party in 2007 after a previous PASOK electoral defeat but handily lost to Papandreou.

A decade ago, he was the minister in charge of Greece's hectic preparations for the 2004 Olympic Games that eventually ran massively over budget.

Ballots opened at 0700 GMT at around 1,000 locations nationwide. [AFP]