Thousands of Greeks, bitterly opposed to further austerity measures, rallied in Athens on Thursday in the first public test for a new national unity government charged with imposing painful tax rises and spending cuts to avert bankruptcy.

The annual rally, which marks a bloody student uprising on November 17, 1973, often becomes a focal point for groups protesting government policies. Unions have said they plan to use it to warn the new government to reverse policies they say have sent Greece into a 'death spiral'.

Students, teachers, workers and pensioners laid wreaths and carnations at the city's Polytechnic school to honour the dozens killed in the 1973 uprising. Leftists, anti-establishment protesters and members of the I don't pay movement were later expected to rally on Syntagma Square outside parliament.

This government will do better (than the last) as long as it is just: crack down on tax evasion and target the rich. But I'm afraid they will cut my pension instead, said 70-year-old Dionysis Samaros, who uses his 720 euro (617 pounds) monthly payment to support himself and his family. How will we make ends meet?

Technocrat Prime Minister Lucas Papademos's three-party coalition won a parliamentary vote of confidence late on Wednesday but the leader of the conservative faction signalled he was already preparing for an election slated for February 19.

Three-in-four Greeks back Papademos, a former vice president of the European Central Bank, but he faces the arduous task of keeping the parties behind reforms required under a 130-billion-euro bailout aimed at preventing a disastrous default.

Greek people and above all the young can overcome the crisis and achieve national targets if they are united and act decisively, Papademos told parliament on Thursday.

He evoked the memory of the 1973 student uprising against the military junta that ruled Greece in 1967-74. Its bloody suppression hastened the collapse of the colonels' dictatorship.

Parliament observed a minute of silence to honour the dead.

The size and mood of Thursday's rally, the first big protest in almost a month, will show the level of anger over the austerity measures sought by Greece's creditors, the European Union and International Monetary Fund.

Many people don't expect any solution, but others hope too much. Deep inside, everyone knows policies cannot change and the measures may be even worse, said Mary Bossis, professor of International Security at the University of Piraeus.

The afternoon march will pass shuttered stores in central Athens to the embassy of the United States, which protesters blame for supporting the six-year military dictatorship.

Greece has witnessed numerous mass rallies against unpopular austerity measures, with some descending into bloody clashes between riot police and demonstrators.

POLITICS

Adding to the mood of uncertainty in Athens, the leader of the New Democracy conservatives -- ahead of rivals in opinion polls -- made clear his support for the new coalition was only temporary, pending an election in February yet to be confirmed.

Antonis Samaras has infuriated Greece's EU peers over the past two years by opposing measures pursued by the then-Socialist government of George Papandreou to stave off default.

In an interview for the magazine 'Epikera' on Thursday, Samaras said his party would not cooperate with its rivals beyond the election and reiterated his call for a switch to pro-growth policies to end a four-year-old recession.

We are working towards an absolute majority to implement our programme without delay and procrastination, he said. When we can, we will change all that needs to be changed. But to do that, we will need a strong mandate in the coming election.

An opinion poll published on Thursday showed Samaras's New Democracy party had widened its lead over the PASOK Socialists with its support rising to 32 percent from 30 in September. The third party in the coalition is the far-right LAOS party.

PASOK fell to 18.5 percent from 24.5, reflecting anger over Papandreou's shock decision to call a referendum over austerity measures already agreed with euro zone leaders.

That move raised doubts about Greece's future in the euro, led to Papandreou's resignation and, after four days of wrangling, Papademos's appointment.

Many Greeks blame the two main parties, dominant since the fall of the junta, for piling up debts totalling 370 billion euros, or 160 percent of gross national product.

Samaras repeated he would not sign a written pledge demanded by Brussels swearing to do what it takes to see through the 130 billion bailout. He says his word is enough.

BUDGET

The government's first task will be to submit to parliament on Friday a 2012 budget of more tax rises and spending cuts.

New Democracy argues tax rises during a deep recession are counter-productive and said data published on Wednesday showing the budget deficit widened by an annual 11 percent in the first 10 months of 2011 backed up its stance.

The European Commission's task force for Greece said on Thursday tax avoidance and lack of compliance had cost the country some 60 billion euros, equivalent to about 25 percent of Greek GDP.

In its quarterly report, the task force -- which coordinates technical aid for Athens -- also commended Greece on its programme of profound structural reform and work towards a more efficient public administration.

Under a key part of the bailout plan, Greece said on Thursday it had begun talks with private sector bondholders on a bond swap which aims to cut some 100 billion euros from the public debt.

Our goal is to structure a transaction that will attract the broadest possible support from the bondholder community, said Evangelos Venizelos, the minister of finance.

(Writing by Gareth Jones; Editing by Sophie Hares)