WASHINGTON (AP) _ For nearly a decade, Ramon Gonzalez Vergara dreamed of leaving Cuba for a better life, but he was afraid to defect on his travels abroad for fear his family would be punished by the Castro government.

Finally, Vergara told a news conference Wednesday, he received his ''lucky break'' when he was assigned to Moscow as Cuba's deputy secretary at the Council on Mutual Economic Assistance, the Soviet bloc's economic confederation.

Vergara, 50, an economist, took his wife, his mother-in-law and his two children, ages 14 and 11, on his foreign posting.

While in Moscow, Vergara and his wife plotted how they would leave the Soviet Union but didn't tell their children about their plan, he said in his first public appearance in this country.

Because it was too dangerous to talk aloud in their Moscow apartment - Vergara feared electronic eavesdropping - he and his wife communicated using chalk on a blackboard.

He said they walked in the park when they wanted to iron out their plans.

Finally, on June 25, the Vergara acted on their plan. The family went to Berlin for a holiday and then crossed the border in a Soviet-made Lada vehicle.

The car worked well, Vergara said, joking that the Soviets ought to be proud of their vehicles.

''We knew we only had a 72-hour grace period,'' Vergara said. The family drove quickly across the continent to Madrid where they had relatives. In Spain, Vergara sought asylum at the U.S. Embassy.

Vergara, whose appearance was sponsored by the Cuban-American National Foundation, is one of the growing number of Cubans who are carrying out plans to leave, said Jackie Tillman, who works with the anti-Castro group.

In his remarks, Vergara said the Soviet Union could not sustain the huge amounts of aid that have propped up the Cuban economy.

''The Soviet aid helps a lot to maintain the standard of living'' in Cuba, he said. U.S. officials estimate the Soviet Union's grants and subsidies to Cuba amount to $5 billion annually, but some private economists say that figure may be high.

Vergara confirmed the $5 billion amount, but he said he doubted it would continue at a time of belt-tightening and shortages in the Soviet Union itself.

''They can't maintain the same levels of past year,'' he said. ''Of course, the Cuban government is aware of the situation; they have felt the first symptoms.'

Vergara, who described Cuba's economy as being in recession, said Havana's trade with the Soviet Union amounts to 75 percent of the total. Trade with former Soviet satellites such as those in Eastern Europe amounted to between 12 percent and 17 percent of the total, he said.

While trade with Eastern Europe has eroded in recent months, Cuba is reaching out to trading partners in Latin America and China, he said.

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