LATIN AMERICA'S most durable dictator, Gen. Alfredo Stroessner, has ruled Paraguay since 1954 with a severity and arbitrariness extreme even by the standards of Latin caudillos. Only recently, and only in response to international pressures, has he begun softening somewhat the still-personal nature of his rule. As a new report (its second) by the International League for Human Rights indicates, what he has done - release some prisoners, improve conditions for others and bring still others to trial - is modest and is reversible at presidential will. Though evidence of emergency is lacking, Paraguay remains in a state of siege.

President Stroessner's reception of league representatives Ben Stephansky (Carnegie Endowment for International Peace) and David Helfeld (University of Puerto Rico School of Law) did mark a revealing change in the climate in which human rights are violated - and defended - since Jimmy Carter entered the White House. The league's first mission to Asuncion, in mid-1976, met official Paraguayan disapproval verging on intimidation. This second mission, in mid-1977, found President Stroessner himself ready to facilitate its inquiry and even to solicit its suggestions for dealing with violations. In turn, the league mission focused helpfully on the further steps needed to regulate the political process by law. Its report is a how-to guide for a dictator wanting to decompress. Offered the opportunity to comment on the report before its release, President Stroessner at first seemed inclined to take up the offer but finally let it pass by.

Some people now wonder if certain Latin American leaders, including Gen. Stroessner, felt they earned a respite from pressure on human rights by presenting themselves at the White House last fall to bless the new Panama Canal treaties. But the Carter administration has quietly stopped the sale of military equipment on official credit to Asuncion. Paraguay's access to development loans has been made subject to political criteria. Gen. Stroessner has felt compelled to accept, some time after his "elections" next February, a mission from the Inter-American Human Rights Commission; this body, unlike the league, operates in a political arena. The general can count on some sympathy there from fellow dictators who cry "anticommunism." He can expect less sympathy from other Latin American military governments moving away from Paraguayan-style crudities. He should get no support at all from the United States - unless he moves in good faith toward the rule of law.