WASHINGTON, Dec. 13— Cuba, a Marxist nation with profound economic difficulties, leads Latin America in primary education, a regional task force has found.

In test scores, completion rates and literacy levels, Cuban primary students are at or near the top of a list of peers from across Latin America, the task force reported.

Indeed, the performance of Cuban third and fourth graders in math and language so dramatically outstripped that of other nations that the United Nations agency administering the test returned to Cuba and tested students again, according to a coordinator of the study.

''They went back to Cuba and retested because there was some anomaly,'' said Jeff Puryear, the co-director of the Partnership for Educational Revitalization in the Americas, which helped organize the task force. ''This is a good, solid, reliable comparison.''

The task force highlighted the results of the first region-wide test of primary students, which was administered in 1998 by the United Nations Education, Scientific and Cultural Organization, or Unesco.

''Cuba far and away led the region in third- and fourth-grade mathematics and language achievement,'' the panel said. ''Even the lowest fourth of Cubans students performed above the regional average.''

Cuba's educational system, along with health care, has been a priority of the government of President Fidel Castro since the early days of the revolution four decades ago.

Critics say Mr. Castro has used education as a tool for political indoctrination. In the past, first-grade reading textbooks have included such revolutionary slogans as ''Study, Work, Rifle,'' and the government frequently mobilizes young students for political demonstrations.

The findings are especially remarkable since the island has lived under an American economic embargo for decades and lost its Soviet patron -- and billions of dollars in subsidies -- a decade ago, plunging Cubans into a period of austerity, blackouts and food shortages. Government planners say they have diverted funds from other areas to bolster schools and hospitals, which nonetheless have deteriorated.

''The question is whether Cuba is going to be able to sustain that system over time,'' said Peter Hakim, the president of the Inter-American Dialogue, a Washington-based forum of hemisphere leaders, which co-sponsored the study.

Resources alone do not explain Cuba's success. Most nations of the hemisphere spend more public money per student than Cuba's allocation of less than $1,000. The United States spends more than $6,000 per student, while Chile, Mexico and Brazil all exceed $1,000, the study said.

''It does show that countries with low levels of national income can still establish quality education for their children,'' Mr. Hakim said.

Some analysts speculated that Cuba's ruined economy has the paradoxical effect of stacking the schools with good teachers. According to that argument, opportunities are so limited that many would-be entrepreneurs and professionals have little recourse but to teach.

The findings for the rest of Latin America were grim. The study, which is to be presented Friday by the president of the Inter-American Development Bank, reported that quality remains low, inequality remains high and few schools are accountable to parents and local communities.