The Reagan administration's threat last week to retaliate against the European Community over new restrictions on U.S. exports was only the latest in a stream of assaults on the community's trade policies.

The EC's policy of subsidizing agricultural exports to dispose of its enormous farm surpluses has come under sharp criticism in recent months from several of the community's major trading partners.

In a particularly strong attack, Australian Trade Minister John Dawkins was quoted as saying last month that community farm exports were "destroying our traditional markets."

Australian officials say the large increase in EC agricultural production has depressed world prices for many key farm products by an average of 16 percent, imposing "substantial costs" on the economies of export-dependent countries such as New Zealand, Canada and Argentina, as well as Australia.

In response to these and other complaints from their trade partners, EC officials have adopted an increasingly defensive tone.

Speaking in Wellington, New Zealand, EC External Affairs Commissioner Willy de Clercq said Wednesday, "I firmly reject accusations that the community's agricultural sector is made up of overprotected, inefficient farmers who are responsible for most of the world's agricultural problems."

The enlargement of the community Jan. 1 to include Spain and Portugal, besides sparking a major dispute with the United States over new restrictions on U.S. farm exports, also has disrupted the EC's relations with its Mediterranean trading partners.

The Mediterranean countries fear that their agricultural exports to the community will suffer from the improved access given to farm products from the Iberian nations as a result of EC membership.

Spain's dynamic agricultural sector is particularly worrisome to the Mediterranean countries, which fear future Spanish production aided by EC development funds. Spain is already the world's leading exporter of oranges and mandarins, and Spanish vineyards are the world's largest.

Morocco, Tunisia and Israel, the Mediterranean countries most concerned with the effects of EC enlargement, rejected conditions offered by the community earlier this year to guarantee continued access to EC markets for oranges, tomatoes, wine and other products.

One high-ranking Moroccan official said during a break in negotiations with the community that to agree to the EC conditions would be the equivalent of signing a "death sentence" for his country. Morocco's exports to the community represent 40 percent of its external trade.

EC enlargement has also disturbed Japan, which usually finds itself the object of community complaints. Japanese representatives to the General Agreement on Tariffs and Trade said last month that Spain and Portugal were imposing new restrictions on a wide range of Japanese industrial products in violation of GATT rules.

As EC diplomats have been busy fighting these various trade fires, the community has suffered new setbacks in efforts to reform the cause of many of the disputes -- the Common Agricultural Policy.

In February, the EC Commission proposed a freeze on guaranteed prices for most farm products and a tax on excess cereal production. The proposal was seen as a modest attempt to slow production and reduce farm surpluses, which must be sold on world markets already glutted by global overproduction.

But in the recent initial round of discussions by EC farm ministers, who have the final say on prices, the proposals encountered opposition from the new French agricultural minister, Francois Guillaume.

The decision by the new conservative government of French Prime Minister Jacques Chirac to appoint Guillaume, a former leader of the largest French farmers' union, was taken by many EC officials as a sign that France would oppose agricultural policy reform.

During the farm ministers' meeting, Guillaume reportedly challenged almost all of the reform plans and told his colleagues: "The first aim of the CAP is to ensure the conditions for higher incomes for European farmers."

Guillaume also alarmed reform advocates by agreeing with West German Farm Minister Ignaz Kiechle that their two countries should develop a joint strategy on agricultural policy.

West Germany vetoed a proposal by the commission last year to reduce guaranteed prices for cereals and has indicated its disagreement with this year's plan for a tax on excess cereal production.