BUENOS AIRES (Reuters) - Argentina's monthly inflation rate is expected to have slowed to 3.5% in September, which would be the lowest monthly rate since the end of 2021, a Reuters poll of economists showed on Tuesday.

That rate would be a sign of progress for the government of libertarian President Javier Milei, which has focused on taming runaway prices since taking office in December.

Projections for last month's inflation ranged from 3.1% to 4.0%, the poll of 27 Argentine and international analysts showed, giving both a median estimate and mean average of 3.5%.

Argentina's national statistics agency will publish the on Thursday.

The September outlook is "very encouraging," said Clara Alesina, an economist at the Fundacion Libertad y Progreso, a think tank. "The slowdown in general and underlying inflation reflects how the markets have reacted positively to the decisions taken."

Consulting firm EcoGO said in a report that several factors helped slow rising prices in September, including a fall in economic activity and an appreciation in parallel exchange rates.

Despite the falling monthly rate of price increases, Argentines still feel the weight of three-digit annual inflation.

Inflation in the 12 months through August reached 236.7%, the highest recorded in the world.

Analysts polled in a central bank survey published last week expect full-year inflation for 2024 at 123.6%.

(Reporting by Hernan Nessi; Editing by Mark Porter)