* Bouteflika, 77, was widely expected to win
* Veteran president rarely appeared after stroke
* Opposition boycotts election seen as fraud (Updates with results)
By Patrick Markey and Lamine Chikhi
ALGIERS, April 18 (Reuters) - Algerian President Abdelaziz Bouteflika, the aging independence veteran already in power for 15 years, won re-election on Friday after a vote opponents dismissed as a stage-managed fraud to keep the ailing leader in power.
Sitting in a wheelchair, Bouteflika had cast his vote on Thursday in a rare public appearance since suffering a stroke last year that raised doubts about whether he is fit enough to govern the North African oil-exporting state.
Preliminary official results showed Bouteflika had won with 81.53 percent of the vote, Interior Minister Tayeb Belaiz told a news conference. His nearest rival, Ali Benflis, won 12.18 percent, and national turnout was 51.7 percent.
Bouteflika, 77, was already widely expected to win with the backing of the powerful ruling Front de Liberation Nationale (FLN) party, which has dominated the political system since independence from France in 1962.
Western governments have been allied with Bouteflika in their campaign against Islamist militants in the Maghreb and are keen to secure Algerian gas shipments to Europe especially with Ukraine's crisis threatening Russian supplies.
Bouteflika did not campaign himself, but loyalists praise him for guiding Algeria out of a 1990s war with Islamists that killed 200,000 people. The conflict left many Algerians wary of the turmoil that has swept neighbouring Tunisia, Egypt and Libya since their "Arab Spring" revolts in 2011.
Six opposition parties boycotted Thursday's vote, saying it would not reform a system mostly closed to change since the FLN's one-party rule in the early post-independence years.
Bouteflika won 90 percent of the vote in 2009 and 85 percent in 2004, when his main rival then, Benflis, alleged fraud on an "industrial" scale.
Many Algerians say ageing FLN leaders, business magnates and army generals - known as "Le Pouvoir" or "The Power", in French - have long managed politics in behind-the-scenes negotiations and see themselves as guardians of stability.
Bouteflika in the past had said it was time for his generation to step aside, but his appearance in a wheelchair at a polling station was a striking image for many Algerians.
"It came as a shock to see a man sitting in a wheelchair to vote while seeking to run a large country for five years. It's not good for the image of Algeria," said Mohamed, a 26-year-old university student.
Algeria mostly escaped the "Arab Spring" unrest that has toppled long-standing leaders in the region since 2011.
Some Algerians point to the 1980s when the FLN opened up one-party rule to opposition and brought an Islamist party close to election victory. The FLN suspended the vote, and the country slipped into more than a decade of war.
Riots and protests are common among younger Algerians frustrated over joblessness, economic opportunities and housing shortages. But widescale anti-government protests are rare in Algeria.
A small movement, called Barakat or "Enough" in local dialect, emerged after Bouteflika's re-election bid to call for peaceful change, though its numbers were limited.
With around $200 billion in foreign reserves from energy sales, the Algerian government spent heavily in 2011 on subsidies, cheap credits and housing to calm rioting over food prices.
Analysts say that after years of state-controlled policies, the OPEC member state needs reforms to open up its economy to more foreign investment and attract more big oil operators to revive its stagnant energy production. (Additional reporting by Hamid Ould Ahmed; editing by Mark Heinrich)