MANILA (Reuters) - Philippine economic growth likely eased in the third quarter as the impact of election spending waned, a Reuters poll showed, but is still expected to be robust enough to keep the Southeast Asian nation as one of the region's outperformers.

On a quarter-on-quarter basis, GDP is expected to have grown 1.1 percent in July-September, which marked the first three months of President Rodrigo Duterte's term in office, after a 1.8 percent expansion in April-June.

Forecasts from five of 15 analysts who gave quarter-on-quarter estimates ranged from 0.8 to 1.5 percent.

From a year earlier, the economy likely expanded 6.7 percent, slowing from the 7.0 percent annual climb in the second quarter but within the government's 6.3 to 7.3 percent forecast for third-quarter GDP.

Economic Planning Chief Ernesto Pernia said on Tuesday the 3 percent growth in farm output in the third quarter makes an above 7 percent economic growth during the period likely.

Duterte has inherited an economy that has enjoyed 70 quarters of uninterrupted growth, buoyed mainly by strong domestic demand.

The 71-year old leader promised to boost the country's growth trajectory to 7-8 percent during his six-year term by raising infrastructure spending and ensuring peace and order.

The central bank has kept policy settings steady since a 25 basis point hike in its key rate in September 2014, but will probably start raising rates in 2017 if inflation picks up as expected, some analysts have said.

(Reporting by Karen Lema; Editing by Kim Coghill)