By Lucinda Elliott

MONTEVIDEO (Reuters) - Voters in South America's laid-back Uruguay, known for its beaches, legalized marijuana and stability, will head to the polls on Sunday in a second-round presidential race between moderates that closes out a bumper year of elections.

The vote in the small nation of 3.4 million people sees opposition center-left candidate Yamandu Orsi take on continuity conservative runner, Alvaro Delgado, who has the backing of a third-placed ally.

Final opinion polls suggest the Nov. 24 runoff promises to be razor tight, with fewer than 25,000 votes potentially separating the frontrunners.

Unlike sharp right-left divides in recent elections in Argentina, Brazil or Mexico, Uruguay's political arena is relatively tension-free, with significant overlap between the conservative and liberal coalitions vying for office, taking some of the sting out of Sunday's final result.

Ballot stations open at 8 a.m. (1100 GMT) and close at 7:30 p.m. local time, with first results expected two hours later.

Orsi, who has pledged a "modern left" policy approach, won 43.9% of the October vote for the Broad Front and will face Delgado, who secured 26.8% but also has the backing of the conservative Colorado Party that together with his National Party made up almost 42% of votes. The two parties did the same in 2019, winning the election.

Orsi has sought to reassure Uruguayans that he does not plan a sharp policy shift in the traditionally moderate and relatively wealthy nation.

Delgado meanwhile has asked voters to "re-elect a good government," seeking to capitalize on the popularity of President Lacalle Pou, who constitutionally cannot run for immediate re-election.

Neither coalition has an absolute majority in the lower house following October's elections. But Orsi's Broad Front won 16 of 30 Senate seats. He argues his senate majority places him in a better position to lead the next government.

Both contenders on Sunday are hoping to attract the roughly 8% of first-round voters who went for smaller, unaligned parties, as well as those who failed to turn out in October.

But neither has made new pledges in the final weeks to appeal to them, and pollsters say a televised debate on Nov. 17 appears to have had little effect.

"I don't know who I'm voting for," said Rosario Gusque, 42, from the region of Canelones where Orsi was previously mayor. "Even less so after seeing the debate."

One question as the biggest year for elections in history comes to an end is whether Uruguay will buck a global trend of incumbent parties losing vote share compared with the previous election. Voters hurt by inflation and high living costs have punished parties in power, including in Britain, Japan and the United States.

A robust Uruguayan economy though could help Delgado on Sunday: "There are few indications that voters are clamoring for significant political change," said Uruguayan analyst Nicolas Saldias of the Economist Intelligence Unit.

(Reporting by Lucinda Elliott in Montevideo; Editing by Daniel Wallis)