BUENOS AIRES, April 1, 2008 (AFP) - Tens of thousands of Argentines rallied outside President Cristina Kirchner's office Tuesday in support of her tax hike on soy exports and against a farmers' strike that in three weeks has emptied store shelves of staples.

'Let the food get through to the people, let the supplies get to the factories, let the merchandise get to the stores,' Kirchner said over the loudspeakers, during her first massive show of support since she was elected in December.

Thousands of farmers, angered by the sharp tax hike on soy exports, Argentina's economic mainstay, announced on March 11, set up some 400 road blocks with tractors around the country, bringing truck deliveries to a complete halt.

Despite a pot-clanging show of support for the strikers a week ago in Buenos Aires, most residents of the capital and other big cities are now faced with a dire shortage of milk, meat and other staples that is slowly straining the country's social fabric.

Kirchner on Monday signed into law the tax hike measure -- from 33 to 44.1 percent -- in defiance of the strikers. The farmers announced they they were prepared to allow trucks to deliver much needed food to city dwellers while they discussed their next step in their protest.

'Hang tough Cristina, don't give in,' shouted supporters crowd gathered at Plaza de Mayo outside the Casa Rosada presidential palace.

Other demonstrators carried signs criticizing 'the landowners' oligarchy,' 'the big financial and economic groups,' and in one reference to the 1976-1983 military junta that ruled the country, 'the putschists of the dictatorship.'

Kirchner and other ministers have labeled the striking farmers 'extortionists,' and said that sky-high commodities prices on the world market, coupled with Argentina's devalued peso, have made many rural landowners very wealthy.

Kirchner has justified the soy export tax increase as a means to have farmers share their newly found wealth with the rest of the population, in her attempt to resolve the biggest test so far of her mandate.

Farmers complain the tax hike, combined with income taxes, transport costs and the high cost of land, would push many of them out of business.

The government's new tax on soy and sunflower products would skim 10 billion dollars off an estimated 24 billion dollars a year farmers stand to make from their profitable exports.

With her husband and former president Nestor Kirchner (2003-2007) standing beside her, Kirchner called on the strikers to respect the authority granted her in last year's election, and told her followers 'I won't betray you.'

'Let's not waste this historical opportunity. We're living in the greatest period of growth in 200 years,' she added, referring to the economic renaissance that began under her husband ending long years of economic depression.

She compared the farmers' strike to a lockout by business leaders in 1976 that preceded the military coup and their infamous 'dirty war' against leftist insurgents.