* President's party has big lead in exit poll
* Partner in previous coalition in second place
* Armenians hope for stability to boost economy
* Region important transit route for oil and gas (Updates with final exit poll results)
By Hasmik Mkrtchyan and Margarita Antidze
YEREVAN, May 6 (Reuters) - President Serzh Sarksyan's Republican Party will keep its grip on power after a parliamentary election in Armenia on Sunday, final results of an exit poll showed after voting ended in the South Caucasus country.
The exit poll released by Gallup International Association put the party on course to win more than 43 percent of the votes in an election that passed off without any of the violence that marred the last national poll in 2008.
Its main partner in the previous coalition, the Prosperous Armenia party led by businessman Gagik Tsarukyan, was in second place on more than 29 percent of the votes, it showed.
The Central Election Commission was expected to start receiving initial results from polling stations across the country of 3.3 million by midnight (2000 GMT). Turnout exceeded 62 percent of eligible voters, it said.
Many voters and Armenian leaders had hoped the election would be a landmark for democracy after voting irregularities marred the last parliamentary election in 2007 and clashes killed 10 people after the presidential vote in 2008.
More than 300 international observers from the Organisation for Security and Cooperation in Europe monitored voting and will give their initial verdict on Monday.
One observer said privately there had been some violations, but it was clear how widespread or serious they were.
Ink stamps on the passports of people who had already voted had disappeared within 15 minutes, giving them the chance to vote again, the observer, who did not want to be named, said, citing several such reports.
The exit poll suggested three parties apart from the big two were likely to win the five percent of votes needed to enter parliament in the former Soviet republic.
The Armenian National Congress, an opposition coalition led by former President Levon Ter-Petrosyan, might also cross the seven-percent threshold set for blocs of parties to win seats, it showed.
There were no reports of violence, an encouraging sign for a country that wants stability to boost the economy, devastated by a war with neighbouring Azerbaijan in the 1990s and then the 2008-2009 global financial crisis.
Voters trickling to the polls in bright sunshine hoped the election would be a landmark for democracy after criticism by international observers over Armenia's elections since the end of communist rule.
"I hope that not one or two, but several parties will be elected. It will help there to be discussions in the new parliament and laws adopted for the sake of people," Gohar Karapetyan, a 48-year-old teacher, said after voting at a school built in the Soviet era and decorated with the national flag.
The parties made social problems and economic issues the main issues of an election campaign that was unusually active for Armenia, Russia's main ally in the South Caucasus.
There were no major differences in their economic programmes, which call for more active development of domestic industry and continuation of cooperation with Russia as well as international financial organisations.
A blast at a campaign rally injured about 150 people on Friday, briefly raising fears of violence, but emergency officials said it was caused by gas-filled balloons exploding.
Armenia nestles in mountains of a region that is emerging as an important route for oil and gas exports from the Caspian Sea to world markets, although it has no pipelines of its own.
Although a ceasefire was reached in 1994, its conflict with Azerbaijan over the tiny Nagorno-Karabakh region remains unresolved and a threat to stability.
Relations with another neighbour, Turkey, are also fraught because Ankara does not recognise the killing of Armenians in Ottoman Turkey during World War One as genocide. (Editing by Louise Ireland)