Opinion polls give Sarksyan, a trusted ally of outgoing President Robert Kocharyan, more than 50 percent support in the vote, which investors say will be a test of stability for the tiny Caucasus nation.
The opposition says the campaign has been unfair and has vowed to take to the streets if it detects vote-rigging. Previous elections in Armenia have been followed by mass opposition protests alleging ballot fraud.
Voters trickled to polls as they opened at 8 a.m. (11 p.m. EST Monday). Polling stations close at 8 p.m. in the country of 3.2 million people and first results are expected on Wednesday.
Armenia, high in the Caucasus mountains, is in a region emerging as a transit route for oil exports from the Caspian Sea to energy-hungry world markets.
Most observers predict that if Sarksyan is elected, his rule will be broadly a continuation of Kocharyan's 10 years in office.
Kocharyan, 53, is barred by the constitution from serving a third consecutive term. He is expected to remain influential, but has refused to disclose what role he will take until his replacement is inaugurated.
Polls give Sarksyan a lead over the rest of the field, led by former speaker of parliament Artur Baghdasaryan and Levon Ter-Petrosyan, a former president who was forced to resign in 1998 but is now seeking a comeback.
"If there is a second round I would prefer to fight against Levon Ter-Petrosyan," Sarksyan said on Saturday.
"It will answer many questions and will bring calm to our country ... if there is a second round and Levon Ter-Petrosyan runs, he will lose overwhelmingly."
But some voters disagreed. Engineer Mesrop Yegizaryan, 48, cast his ballot at public school number 24 for Ter-Petrosyan.
"I'm voting for him because he made a lot of mistakes when he used to president. But he's changed a lot since then, and I'd like to support him to give him a chance to rebuild what he has destroyed," he said.
More than 300 foreign observers from the Organization for Security and Cooperation in Europe (OSCE), as well as dozens from the Council of Europe and other foreign organizations, will monitor voting.
Final results must be released within seven days of the vote.
Güncelleme Tarihi: 19 Şubat 2008, 12:40