* PM Orban calls on supporters to prevent return of communists
* Leftist opposition holds much smaller rally
* Orban's Fidesz party leads in polls ahead of 2014 election
By Gergely Szakacs and Krisztina Than
BUDAPEST, Oct 23 (Reuters) - Hundreds of thousands of Hungarians demonstrated in support of Prime Minister Viktor Orban's government on Wednesday as the country marked the anniversary of a 1956 uprising against Soviet rule.
Facing an election in April or May, Orban invoked the spirit of that rebellion to tell his supporters to mobilise for a new battle against the heirs of the communists.
Without referring to any of the leftist parties by name, he said if they took power, they would again hand over the country to foreign "conquerors", in the form of speculators and banks.
"You cannot believe that your government will win this struggle without you and instead of you," he said, calling on supporters to defend the government's signature policies such as pension increases and cuts in utility prices.
"We have no reason for haste, but slowly and surely we must get our machinery rolling and get our troops ready for battle," Orban said in a speech on Budapest's Heroes' Square, where he first made his name by calling for a pullout of Soviet troops in 1989. "Be prepared: we can now finish what we started in 1956."
Orban, 50, heads a conservative government and his Fidesz party leads in opinion polls. At a rival rally, the leftist opposition drew a much smaller crowd of some 15,000 to 20,000.
The 1956 uprising marked the first serious challenge to Soviet domination of Eastern Europe. Though it was crushed, its impact was lasting and it helped to inspire the eventual overthrow of communism in 1989, when Hungary and other Warsaw Pact nations broke away from Moscow's orbit.
The march, whose organisers included businessmen close to the government and right-wing journalists, proceeded across Budapest, with people waving the national flag.
Pensioner Istvan Balogh, 65, said Orban had tackled the country's problems well and represented the people's interests. He contrasted that record with past Socialist governments, which he said had backed multinational companies and banks.
"They had eight years but they destroyed everything and we nearly ended up like Greece," Balogh said.
Orban, who has taxed banks and big foreign business heavily and has nationalised private pension savings to rein in the budget deficit, says his government has saved Hungary from financial collapse since winning power in 2010.
His critics at home and abroad say his government has passed legislation to limit the powers of Hungary's top court and weaken democratic checks and balances.
At the smaller leftist rally, Socialist leader Attila Mesterhazy said the government must be ousted in next year's election as Hungarians were worse off economically and Orban wanted to isolate the country from western Europe.
"He has turned into a despot with greying hair from a young democrat ... He is the one whom we must oust ... and will oust," he told the crowd.
Demonstrator Jozsef Paszti said: "It's obviously visible that Viktor Orban tries to create a bourgeois layer around him, perhaps hoping that they will create jobs, but the price of this is that huge masses of people have become very poor."
In the latest opinion poll, Orban's Fidesz had 29 percent support, while the Socialists, the biggest opposition party, had 14 percent. About 40 percent of voters were undecided. (Editing by Mark Trevelyan)