* 2012/2013 wheat for export now seen at 4.5 mln tns
* Argentina seeks to ensure domestic food supply
* Rains hit harvest in grains powerhouse Argentina
BUENOS AIRES, Dec 8 Major wheat supplier Argentina will trim the quantity of 2012/2013 wheat destined for overseas shipment to 4.5 million tonnes from a previous 6 million due to a smaller than forecast harvest, a local newspaper reported on Saturday.
Argentina's government curbs wheat and corn exports to ensure ample and affordable domestic supplies of food.
The wheat harvest in grains powerhouse Argentina will be smaller than expected and of poorer quality this season as farmers slog through waterlogged fields, trying to save their crops from toxic fungi bred by too much rain.
Argentina's government has already told exporters that include grain giants like Cargill and Bunge that it will reduce the quantity of export permits to ensure local supply, according to La Nacion newspaper.
The announcement comes at a time when world grain markets are contemplating the risk of prolonged supply tensions. Consumer nations have seen their wheat bills soar this year and Argentine supply has been eyed to help cap prices.
A source at an exporter told Reuters the firm's headquarters had asked its local branch to stop buying wheat of the 2012/2013 cycle, but could not confirm if the request was linked to the government's announcement.
Argentina's government forecasts the 2012/13 wheat crop at 11.1 million tonnes, recently marked down from 11.5 million.
But with more than 26 percent of the harvest already collected, yields have been poor, prompting some analysts to reduce their projections for the full crop.
Argentina's new export policy took effect this year. (Reporting By Maximiliano Rizzi; writing by Alexandra Ulmer; editing by James Jukwey)