IN a "protest of despair" whose repercussions are likely to be felt around the world, more than 150,000 French farmers marched through the streets of Paris Sunday, calling for measures to bolster their sagging incomes and reverse an accelerating depopulation of the French countryside.The violence the Socialist government of Prime Minister Edith Cresson had anticipated never materialized. Yet the sheer size of the march will almost certainly influence government policy as France works through three sets of important international negotiations involving agriculture in the coming weeks. With French beef farmers facing hard times after two years of cheap imports from Eastern Europe, the government took a hard line on European Community (EC) plans to further open its markets to Eastern European products. France is also leading the opposition to the EC Executive Commission's plan, now under discussion, to drastically overhaul the Community's $50 billion system of farm supports. In addition, the massive protest is apt to bolster French resolve to stand firm against intense pressure to get international trade negotiations moving again by cutting EC farm-trade subsidies. Last December the four-year-old negotiations, organized by the 108-nation General Agreement on Tariffs and Trade (GATT), collapsed when a French-led EC refused to consider substantial cuts in its $34-billion annual farm-trade subsidies. Agriculture Minister Louis Mermaz said that the march "is a huge support for us as we continue negotiating the future of the Community's Common Agriculture Policy and international trade rules under the GATT." France is also keen on protecting as best it can a sector that provides a $10 billion annual trade surplus to an overall negative trade balance. But the farmers, who invested heavily in land, equipment, and animals in recent years based on high farm prices, have seen their incomes tumble as overpro duction and imports have taken their toll. Protesting farmers said the march was not simply a call for new income supports, but a warning that "the rural life at France's heart" is dying. The number of French farmers, has fallen from about 8 million in 1955 to about 3 million today. But increased productivity has brought a surplus of grain, and to the EC paying farmers to pull land out of production.