ASUNCION (Reuters) - Conservative Paraguayan businessman and political newcomer Horacio Cartes is the leading candidate ahead of the April 21 presidential election, according to a poll published on Monday.

Cartes vows to bring the once dominant Colorado Party back to power after it lost the presidency in 2008, the party's first defeat since democracy was restored to Paraguay in 1989.

With 37.3 percent support, Cartes was clearly favored over Efrain Alegre of the Liberal Party, who got 30.3 percent.

The survey, conducted from March 9 to 15 by research firm First Analisis and Estudios, was published in local newspaper ABC. It said the poll had a margin of error of plus or minus 3.1 percent.

In third place was journalist and local TV host Mario Ferreiro, a left-leaning candidate who polled at 9.5 percent.

The previous leader of the soy-exporting country, Fernando Lugo, was voted out of power last year by Congress for failing to keep the peace after 17 police and peasants were killed in clashes over a land eviction.

Lugo, a leftist and a former Roman Catholic bishop, was a year from completing a five-year term at the time he was ousted.

Lawyers for Lugo questioned the constitutionality of his lightning-quick impeachment. But the country's top electoral court ratified its legitimacy.

(Reporting By Mariel Cristaldo, writing by Hugh Bronstein; Editing by Mohammad Zargham)