Ex-guerrilla and former leader set for Uruguay race

* Ex-guerrilla seen leading leftist ruling coalition

* Former president to represent the right

MONTEVIDEO, June 28 (Reuters) - An ex-guerrilla fighter and a rightist former president will go head-to-head in Uruguay's presidential election in October following primaries on Sunday, unofficial exit polls showed.

Jose Mujica, a folksy senator and ally of Venezuelan President Hugo Chavez, will try to keep Uruguay's ruling leftist coalition in power.

Pollsters said Mujica won between 52 percent and 54 percent of his party's vote, putting him in pole position to succeed President Tabare Vazquez, a moderate leftist who is barred from seeking a second term under the constitution.

He will challenge center-right former President Luis Lacalle, who led the small South American ranching nation in the early 1990s.

The polls said Lacalle won the opposition conservative party primary with between 54 percent and 57 percent support.

Both Lacalle and Mujica are seen as representing a hard-line in their parties and political analysts said they would have to start building alliances to bolster their support base.

The polls showed Mujica triumphing convincingly over former Economy Minister Danilo Astori, who is unpopular among more radical leftists.