Argentine President Cristina Fernandez, mired in a political crisis after 20 days of a farm strike that has caused food shortages, sought to show her resolve on Tuesday with a huge pro-government rally.

Farmers irate over higher soy export taxes have held back goods from market since March 13, making fresh food scarce in the capital and freezing grains exports from Argentina, a top world supplier of soy, corn, wheat and beef.

Fernandez called on farmers to clear roadblocks from highways as she addressed tens of thousands of cheering allies from unions and community and human rights groups.

"Don't do more harm to the people, lift the roadblocks so Argentines can get food," she said.

Farm leaders say they will decide on Wednesday whether to continue their protest at highways all over the country.

Last week Fernandez faced her first major anti-government demonstration, when thousands of middle-class Argentines banged pots and pans in city streets in support of the farmers.

Political commentator James Neilson said Tuesday's rally was intended to show that the government had not been weakened and was backed by public opinion in taking a tough stance against the farm protest.

"They are worried about appearing weak. But by doing this it sends the message you might not be as strong as you'd like people to think," he said.

SOME CONCESSIONS

On Monday, Fernandez offered some concessions to farmers but did not meet their demand that she scrap a tax regime that replaced a fixed levy of 35 percent on soybean exports with a variable rate that is about 40 percent at current prices.

The measures she offered include a rebate for small farmers on the new taxes, plus compensation for transportation costs for farmers far from ports.

But farm leaders said the measures did not go far enough.

With farmers blocking highways and holding back farm goods, chicken, dairy products, fruits and vegetables are scarce in Buenos Aires.

The strike has proved the most serious challenge yet to Fernandez, heightening criticism of economic policies laid out by her predecessor and husband, former President Nestor Kirchner.

Farmers were already angry over government limits on exports to try to control domestic food prices, even though they have benefited from state subsidies on fuel and policies that keep the currency weak.

Fernandez says the higher taxes are a key part of her economic plan to contain inflation on domestic food goods and redistribute wealth from a commodities boom.

Argentina, with vast areas of arable land, has benefited from high international prices for soy and other crops. But Fernandez says the country is in danger of converting too much of its land to soy for export, displacing domestic staples wheat and beef.