ATHENS (Reuters) - Greece's leftist Syriza party was holding a narrow lead of less than one percentage point over its New Democracy conservative rival in the countdown to elections on Sept. 20, a Metron Analysis poll showed on Friday. The poll for Parapolitika newspaper said that 31.7 percent of respondents would vote for Syriza, and 31.3 percent for New Democracy. The result incorporated an assessment of likely voting intentions of undecided voters. (Reporting By Karolina Tagaris; editing by John Stonestreet)