By Elaine Monaghan

WASHINGTON (Reuters) - The United States lodged a formal diplomatic complaint with Cuba on Monday accusing it of stopping people from leaving the communist island even if they had visas for travel to the United States.

``We are expressing our concern that 40 years of Castro's policies have purposely separated family members and this is causing a very real human tragedy,'' a State Department spokesman said after announcing that the note had been issued to the Cuban interests section early on Monday.

He said the problem was illustrated by the fact that some Cubans had been found recently trying to enter illegally on boats and rafts, even though they had a U.S. visa.

The State Department spokesman said that in the past 75 days, there had been 57 cases involving 117 individuals who had U.S. visas but had been refused exit from Cuba.

A spokesman for the Cuban interests section said officials were studying the note and repeated Havana's criticism of a 1966 U.S. law that offers preferential treatment to Cuban migrants who touch U.S. shore. The policy allows Cubans who reach the U.S. to remain in the country but returns to Cuba those stopped at sea.

``Only the criminal, immoral and discriminatory policy of the U.S. government, specifically manifested in the so-called Cuban Adjustment Act, is responsible for the continuing deaths of Cubans who try to reach American soil,'' said Roberto Garcia, second secretary at the Cuban interests section.

Washington observes an economic embargo against Havana imposed in 1962 after Fidel Castro's 1959 revolution. Already rocky relations entered an even stormier phase last year with the fight over 6-year-old Cuban shipwreck survivor Elian Gonzalez.

The child survived a shipwreck in November that killed his mother and 10 other people fleeing Cuba only to become entangled in a long legal battle between his Cuban father, who wanted him returned home, and Miami relatives, who wanted him to remain in the United States. In the end the father prevailed.

The diplomatic note, delivered early on Monday, came amid a hiatus in talks on migration following the Gonzalez case.

The United States bans its citizens from traveling to Cuba as tourists though it does allow journalists, religious and human rights workers, and cultural and academic groups to go there if they get special permits first.

In a bid to ease the problem of illegal migrants risking their lives to travel to the United States, the two countries signed agreements in 1994 and 1995 under which Washington was to issue at least 20,000 visas a year for permanent migration.

The United States blames the exodus of Cubans on the Castro government's failed socialist economy, its restriction of basic liberties such as the right to travel freely, and Cubans' desire to be reunited with families in Miami.

But ever since the Gonzalez case hit the headlines, Havana has stepped up its criticism of the embargo and the 1966 policy that it blames for deaths of Cubans trying to make the perilous 90-mile (145 km) voyage by sea to the Florida coast.

Earlier this month Cuba's ruling Communist Party daily wrote a front-page editorial calling the policy ``murderous'' after two Cuban brothers were mutilated by sharks while trying to reach Florida illegally.

The State Department spokesman said the U.S. also noted its concern that Cubans, earning about $10 a month on average, had to pay $600 to leave the island -- $400 for a medical exam, $50 for a passport and $150 for an exit permit.

In June, the State Department said Cuba had postponed indefinitely talks on migration that usually take place every six months and had been scheduled to start on June 27. Copyright © 2000 Yahoo! Inc., and Reuters Limited.