President Francois Mitterrand today expressed "serious reservations" about the Reagan administration's Central America policy and said he was an uneasy about Washington's attitude toward the underdeveloped world as about its "unbearable" high interest rates.

In an interview with Le Monde -- his first with a French newspaper since becoming president -- he stressed his belief in American leaders' "capacity for reflection," but said that people in Central America "wanted to get rid of oligarchies that, with the backing of bloody dictatorships, exploit and crush them in insane conditions."

Arguing that uprisings were understandable when a "tiny proportion of the population owns almost all the property," Mitterrand said the problem was not of "communist subversion" -- as the Reagan administration has argued -- "but of a refusal of poverty and abasement."

"The West would be better advised to help these people than to force them to remain under the jackboot," he said. "When they cry out for help I would like [Cuban President Fidel] Castro not to be the only one to hear them." l

American officials who have had intensive recent contacts with French officials have let it be known here that the Reagan administration is seriously concerned about this kind of French approach, especially were it to become translated into militant policy.

These officials have left the impression that such policy differences on Central America -- and to a lesser extent concerning southern Africa -- could be as damaging to bilateral relations as Mitterrand's inclusion of four communist ministers in the new French government.

One of Mitterrand's more controversial appointments prior to the appointment of the communists was that of Regis Debray, the former guerrilla war theorist who spent three years during the 1960s in a Bolivian jail for guerrilla activities alongside Che Guevara. Debray was named an adviser to Mitterrand on foreign policy, particularly the Third World. Some French militants maintain that Debray has become "bourgeois" since the days he traveled with Guevara.

The French president's wife, Danielle, who shares her husband's interest in Third World causes, belongs to the Salvadoran and Latin American Solidarity Organization, a Socialist Party group. It has helped victims of the civil war in El Salvador. In a press statement after her husband's election, Danielle Mitterrand said, "I will not give up my role as an activist within humanitarian organizations, both national and international."

Mitterrand's approach to U.S. policy in Central America, particularly in El Salvador, differs sharply from that of his predecessor. Although former president Valery Giscard d'Estaing's government cautioned against U.S. troop involvement there, it privately expressed its willingness to support less drastic forms of U.S. involvement.

Since the Reagan administration decided last February to "draw the line" against Soviet-Cuban expansionism in El Salvador, it has sought backing from NATO nations and other allies. Although West Germany's Social Democratic leadership was uneasy, no major U.S. ally until now has voiced such public reservations about U.S policy in Central America.

Mitterrand sought to play down differences with the United States over the Communist ministers by thanking Vice President George Bush for his "open, sympathetic, constructive" approach and "his real courtesy" during their meeting here last week.

Especially appreciated was Bush's decision to tell him that he would be informing the press upon leaving Mitterrand of the administration's concern over the Communist ministers and in writing a letter of thanks at the end of the vice president's Paris visit for having received him.

"There's nothing shocking about your allies having trouble understanding the reasoning behind your acts," Mitterrand said, drawing a distinction again between Bush's approach and the harsher State Department statement.

Mitterrand argued that to have excluded the communists -- who emerged much weakened from the Socialist sweep in parliamentary elections -- would "hurt millions of people by excluding them from French political life when they only asked to be respected." However, he said the "ideological conflict" between Communists and Socialists had not ended.

Returning to relations with the United States, Mitterrand said, "You cannot hope for greater political and military homogeneity and content yourself with an everyone-for-himself approach in economics."

Addressing his most important economic grievance against Washington, Mitterrand said he expected no interest rate relief in the next six months. But he said that "it is possible to discuss" the problem with the United States and thus reduce the length of time required for cutting them back.

Mitterrand reiterated his now standard support for the American-backed Camp David agreements between Egypt and Israel.

However, despite his close ties with Israel, Mitterrand indicated that it is up to the Jewish state to tackle the Palestinian problem in "a more positive way."

"Every people has a right to a land," he said, apparently referring to the Palestinian desire for a homeland.