SANTIAGO, Dec 16 (Reuters) - Chile"s ultra-right presidential candidate Jose Antonio Kast and leftist Gabriel Boric appear to be tied among likely voters ahead of the country"s polarized runoff election on Sunday, according to a poll seen by Reuters on Thursday. Kast, who won a partial majority in the first round on Nov. 21, has 48.5% of the voting intention, ahead of Boric with 48.4%, according to a survey of 2,218 potential voters conducted by consulting group AtlasIntel. When non-valid votes are removed, each candidate would end up with 50% of the vote. A little over 15 million Chileans can vote in Sunday"s election. In the first round, Kast, a conservative lawmaker, won 27.9% of the votes and Boric 25.8%. The first opinion polls after the initial round favored leftist politician and former student movement leader Boric by several points, but that lead has diminished in recent days. In AtlasIntel"s previous poll, which surveyed 2,692 likely voters at the beginning of December, Boric had led with 41% versus Kast at 38.7%, or by 51.5% versus Kast"s 48.5% when only valid votes were counted. The country is in a two-week blackout period where pollsters cannot publicly publish surveys on the vote, but private polls are often commissioned.