BUENOS AIRES, Jan 24 (Reuters) - Recent rains in Argentina surpassed the "most optimistic" forecasts, the Rosario grains exchange said on Tuesday, a boost for grains farmers in the country hit by drought, though rainfall was unevenly spread and more is needed.

Argentina, the world's top exporter of processed soy and No. 3 for corn, has been battling one of the worst droughts in decades that has hammered crop harvest forecasts.

Recent rain has brought some relief, and although it was too late for the country's wheat crop, it could help support 2022/23 soy and corn yields.

"Argentina, undergoing the most significant drought in the last 60 years, received higher rainfall volumes than expected," the exchange said in a report.

It were said the most intense rain storms had been over La Pampa, northwest of Buenos Aires and finally in Salta, with 127 millimeters (5 inches) in the provincial capital.

Overall, however, only 15% of the Pampas region received rainfall above the key level of 45 mm. The Buenos Aires area received 15%, La Pampa 10%, Santa Fe 5% and Cordoba 3%. Some areas got none at all.

"The variability was extreme. There are locations with more than 100 mm and others where it did not rain," the exchange said.

"To reverse the state of drought and move to optimal reserves in the soil, the (regions) would need precipitation values of 160 to 180 millimeters." (Reporting by Adam Jourdan Editing by Sandra Maler)