The Haitian Army made widespread arrests of politicians, human rights activists and journalists in the island's capital of Port-au-Prince Friday night and into yesterday morning, according to the State Department and sources reached in Haiti.

The crackdown, according to scanty reports from Haiti, included at least 50 people and "virtually every opposition spokesman or rights activist in the country."

It was the largest since former president Francois "Papa Doc" Duvalier went on a rampage against perceived opponents in 1963, and it far surpassed any similar action by current President Jean-Claude Duvalier, who took over after his father's death in 1971.

The State Department said it had received "reliable reports" of the arrests that "if true, are a cause of great concern. We would view an attempt by the Haitian authorities to silence the free expression of political opinion as inconsistent with the government's previous expressions of an intention to move toward a more liberal system."

A Department spokesman said, "We have expressed our concern to the Haitian ambassador in Washington, and we will also express it to appropriate officials in Port-au-Prince through our embassy. It is our hope that those arrested will without further delay or harm be freed or, if they are charged, bail will be considered."

Included in the arrest sweep were Gregoire Eugene, head of what the State Department called the "responsible Haitian opposition party, the Christian Socialists;" Joseph l'Enfantin, a founding member of the Haitian Human Rights League; family members of Christian Democratic leader Silvio Claude, who was arrested last month, and managers and staff members of Haiti's three leading radio stations, Radio Progress, Metropole and Haiti-Inter.

Sources said the Army was still seeking Radio Haiti-Inter commentator Jean Dominique, whose broadcasts have critized the government for its treatment of Haitian peasants and for lack of political freedom.

Members of the Haitian exile community speculated yesterday that what appeared to be a well-planned Army offensive had been held off until the end of the Organization of American States General Assembly here, where last week a highly critical report on Haiti's human rights record was presented.

They, together with attorneys and U.S. human rights activists, also charged that the crackdown was a reaction to the election of conservative Ronald Reagan, who they believe has signaled an upcoming reversal of the Carter administration's policy of sanctions on human rights issues.

A Haitian official who was reached by telephone but asked not to be named said that internal pressures had led to the crackdown. Haiti's old guard of government leaders are believed to resent Duvalier's announced liberalization plans.