By Hernan Nessi

BUENOS AIRES Argentina's monthly inflation rate is expected to slow to 7.0% in June, according to the median forecast in a Reuters poll, after hitting 7.8% in May, as the government battles to control spiraling prices ahead of elections in October.

The poll of 23 analysts measures inflation by the Consumer Price Index (CPI), with estimates ranging from 6.6% to 7.8%.

South America's second-biggest economy has suffered sky-high inflation over an extended period, with the annual rate well over 100%, which has contributed to a prolonged economic slump exacerbated by the steady erosion in the value of the local peso currency.

Consumer prices surged 7.7% in March, 8.4% in April, and 7.8% in May, among the highest figures in the world, according to official data from national statistics agency INDEC.

Rising food prices in June are expected to be similar to May, while other areas are seen easing compared to April, according to Federico Zirulnik, economist for the Scalabrini Ortiz Center for Economic and Social Studies.

Still, analysts project inflation will spike once again in July.

"For next month we expect the index to show a new acceleration, not only due to the seasonality of the month itself, but also due to a new adjustment in regulated prices... in public transport, fuel, prepaid, education, among others," said the Freedom and Progress Foundation.

The ruling center-left coalition of outgoing President Alberto Fernandez faces an uphill battle this year to hold on to power, weighed down in large part by the country's ailing economy.

INDEC will release official June inflation data on Thursday at 1900 GMT.

(Reporting by Hernan Nessi, writing by Isabel Woodford; Editing by Emelia Sithole-Matarise)