UPDATE 5-Argentine farmers to resume protest over grains tax

(Adds cabinet chief's comment, new De Angeli quote)

By Nicolas Misculin

BUENOS AIRES, May 7 (Reuters) - Argentine farmers announced fresh protests against a tax hike on Wednesday, aiming to put pressure on the government by disrupting grains exports from one of the world's top suppliers of corn, wheat and soy.

Farm leaders said they had decided to break off weeks of tense negotiations with the center-left government because officials were unwilling to reform a new system of grains exports taxes that triggered a three-week strike in March.

"After 57 days, we haven't advanced. The government has chosen the road of confrontation. It's the only reason we haven't reached an agreement," said Eduardo Buzzi, president of the Argentine Agrarian Federation, one of the four groups that led March's strike.

That protest caused food shortages in Argentina's supermarkets and landed President Cristina Fernandez with her biggest challenge since taking office five months ago.

It also hit grains shipments, and U.S. soy futures soared on Wednesday as the specter of fresh disruption loomed.

At a joint news conference, agricultural leaders said the freeze on selling goods such as corn and soybeans would last until May 15, but added that farmers would not block highways because they did not want ordinary Argentines to suffer.

Farmers manned roadblocks and halted sales of grains and beef for 21 days in March after the government introduced a sliding scale of export taxes that substantially raised the levies on soy and sunseed products.