By the time he was 10 years old, Isidro Ortega Jr., now 22, had learned to reassemble a stripped-down Polish submachine gun, read Marx and been asked to spy on his family.

Olga Ortega's eyes narrow with rage at what was done to her two sons in the name of the Cuban revolution.

"You know, they used to come into the school and say, 'Children, close your eyes and pray to God to give you ice cream,'" she recalls. "The children prayed and then they told them to open their eyes and, of course, there was no ice cream.

"Then theysaid, 'Children, close your eyes and pray to Fidel Castro for ice cream.' So they closed their eyes and when they opened them there was ice cream. 'Now you know who takes care ofyou,' they said."

She flips through an old family album, one of the few belongings the Ortegas were permitted to takewhen they fled Cuba in 1968. Past the pictures of her sonsin their school uniforms -- miniature military fatigues -- past the pictures of relatives left behind and relatives wasdead, the Havana skyline in the background. Then she shutsit abruptly.

"No," she says, "Even if Castro left Cuba today, I could never go back now. Her pained face suddenly brighttens. "I'm American. I can't even eat Cuban food anymore."

For the more than 30,000 Cubans in this aging community of 60,000 across the Hudson from the Manhattan skyline, the bitter memories of what happened in their homeland are slowly fading. They are too preoccupied with making their way in their new land.

But while the longtime residents here see the Cubans as only the latest in the successive waves of immigrants -- German, then Irish, than Italian -- who first beached in Union City on the way to becoming Americans, the Cubans say their reasons for coming make them unique.

"We didn't come just because there were jobs here," said Ibrael Suarez, 50, who came in 1970. "I had a relatively good job as an agricultural expert. I even had a car for my job. I came because I was not a communist and I wanted to raisemy family the way I wanted to raise it, not the way the government wanted me to raise it."

Whatever their reasons forcoming, the Cubans have transformed this city.

Afer Italians, the last immigrants to call it home, moved up the economic ladder and then moved out, the Cubans bought the storefronts left vacant. They put up signs advertising ropas (clothes) and zapatos (shoes). They worked in factories during the economic boom in the 1960s. They bought homes that had been vacant for years and pushed up property values.

"When they started to come in the 1960s this place was dying," says Galto Serafino, a Union City realtor and native, the sonof an Italian immigrant. "There were apartments available, storefronts available. There was room. And we were glad to see them come."

"Now there's not an area you can go to and not find a Cuban," says Jim Lagomarsino, another Italian American raised in Union City. "They'll use this place justlike our families did. A steppingstone. A doorstep to America."

Overall, the Cubans have been remarkably successful.

According to a Cuban Planning Council survey, roughly one out of every five Cuban wage earners here is classified as a professional or manager. The median Cuban family incomein this somewhat depressed area is $14,555. While the national unemployment rate is 7.7 percent and the local rate is nearly 10 percent, only 6.7 percent of the Cubans here are unemployed.

Proportionately fewer Cubans are on welfare than members of other ethnic groups. They pay taxes on time, giving Union City one of the highest collection rates of return in the area. And they look after their own by contributing thousands of dollars toward the resettlement of new refugees and giving them clothing and old furniture to start them off.

Some Cubans, who apparently had connections with organizied crime in the old pre-Castro Cuba, are reportedly using Union City as a distribution center for narcotics coming from Miami, police say.

"There have been a few involvedin heroin traffic," said Capt. George Yannuzzi. "But we think they're hangovers from the old days when the Mafia was thinking of making Havana the gambling capital of the world.There are bad ones in any lot."

Police in Union City are quick to point out that only a handful of the Cubans has ever been suspected of having any connection with the drug trade.

Part of the economic success is attriibutable to the sheer numbers of Cubans who have come to the United States and Union City in the last 20 years -- at least 855,000 nationally, not including the 117,000 who came by boat earlier this year. The large Cuban communities that resulted softened the cultural shock many new arrivals might otherwise have experienced.

At the same time, the strong cultural and business ties Cuba had over the years with the United States have given most Cubans an insight into American viewpoints, an adjustment asset that most other immigrants and refugees lack.

Yet there are problems. Many older Cubans have great difficulty in learning English, a handicap that keeps them rooted in low-paying blue-collar jobs where there are large numbers of other Spanish-speakers. The resulting isolation causes problems, but because of pride, few take advantage of mental health services.

The nation's economic ills are affecting the Cubans, too. Those who don't speak. English cannot find new jobs easily. The community -- both Cuban and non-Cuban -- is also nervous about the possible impact on the job market of the 10,000 to 12,000 new Cuban refugees expected to settle in Union City in the next few months.

The increased competition for jobs also worries some who fear that it will prompt an increase in latent anti-Cuban sentimentfelt by a few longtime residents and the growing number of Puerto Ricans in the area, who also are affected by the nation's economic woes.

"You've got to be Spanish-speaking toget a job," said Billy Metzner, 24, a machanic whose familycame as German immigrants to Union City. "The Cubans, theycome over, they get everything. We Americans don't get nothing. The companies would rather have the Spanish working for them because they work for peanuts."

There is no denying the overwhelming Cuban presence in the community. The language on the streets is Spanish. Stores advertise their goods in Spanish, a few noting in their windows: "English spoken here." Even the menus in Chinese restaurants are in Spanish, and the Chinese owners speak Spanish far more easily thanEnglish.

It is within this tightly knit ethnic community, reminiscent of the Little Italys and Irelands of the past,that families like the Ortegas and Suarezes are steadily climbing upward. But it has not been easy.

When Ibrael Suarez brought his mother and father, his wife and three daughters to Union City from Camaguey, Cuba, he was penniless. His lack of English, plus his lack of documents attesting to his education in agriculture (the Cuban government refused tolet him take them with him) left him no choice but factory work.

Like most of the Cubans here, he came because friends and family had come before him. With their help, he rented a small apartment for $150 a month, took a $110-a-week job, and began the time-honored economic climb of the immigrant.

Today he earns about $240 a week working for a wire company. He has a 4-year-old son, born in America, and his daughters are graduating from high school with thoughts of going to college. He has recently moved to the suburbs to renta house owned by his brother who once lived in Union City himself.

"There are things I have learned," he says. "Happiness is not here anymore than anywhere else. It is not all like we Cubans would have wanted it to be. Yet, we have everything we need. We live, practically speaking, well. Weeconomize so the children can get a good education. The American dream exists. We can live happily. There is work."

The Ortegas are on their way up, too. When Olga and her husband Isidro Ortega came to Union City a dozen years ago from Spain, the only country to which the Cuban government would allow them to emigrate, they had $5 and some family photoalbums of life in better times in Havana.

Today they owna small frame house in Union City that they bought from another Cuban two years ago for $37,000, using money they had saved diligently for years. "I think it is worth about $6,000 more today," said Mrs. Ortega proudly.

They give clothing and old furniture to the new crop of Cuban refugees, justas more established Cuban families offered them hand-me-downs when they first came.

Isidro Ortega was a traffic policeman in Batista's government when Castro came to power. Itwas a black mark against him. Mrs. Ortega worked for a novelty store that sold items to American tourists. That also made her suspect in the communist government's eyes. After Castro solidified his power, she was thrown out of work and never permitted to hold a job again, while her husband was forced to work as a cab driver, using the old American car hehad purchased before the revolution.

But his policeman past caught up with him, and the government sent him to a forced labor farm camp for 14 months.

When the Ortegas finally arrived in Union City -- a cousin was here already, providing them with a tie to the community -- Ortega went to workfor a chemical company. Mrs. Ortega went to work for a cosmetics firm. Within six months they had saved enough to open a small restaurant in Union City, but the work proved too hard and they sold it a few months later.

"I was making about $1.65 a hour when we first came, and my husband was earning about $2.30 an hour," she said. "So we earned about $160 a week between us. We rented a little apartment here forabout $135, spent about $37 a week on food and felt good."

Eight months after they came, they had also saved enough to buy a $200 used car that they kept for just over two years. Mrs. Ortega went to work for a small baby toy company called Danara Inc., where her two sons now work as well, and her husband found a job in another factory.

Today they own a 1972 compact car they bought a year and a half ago -- "it gets better gas mileage," explained Mrs. Ortega -- a house that has an apartment they rent to another Cuban family, and they earn about $530 a week between them. Their own sons live at home and contribute $50 each a week toward household food and expenses.

The Ortegas and Suarezes are fairly typical of the success and social circumstances of Cubans in theUnited States, according to studies done by Prof. Barry Chiswick of the University of Chicago, and Prof. Alejandro Portes of Duke University.

According to Chiswick, who compared Cubans to European immigrants, the Cubans start on lower rungs of the economic ladder than do the Europeans. But after about 10 to 12 years, their earnings equal or begin to exceed the earnings of the Europeans.

Portes found, in a study of Cubans who came to Miami in 1972 and 1973, that unemployment is extremely low -- 4.4 percent as of 1979. At the same time, 40 percent of the sample work either for Cuban-owned businesses or are self-employed.

"They have an overwhelmingly positive attitude toward . . . the United States," he said. "Their original gratitude has not given way to skepticism." He said that the Cubans' success is deeply rooted in the Cuban community and few, as a result, speak English well.

"An entire life can be conducted within the bounds ofthat conclave," he said.

Isidro Ortega Jr. is convinced that his family is making the kind of progress that they should, though he feels the older generation sticks together much too much and spends too little time learning English.

"We subscribe to three papers," he said. "I read The New York Times and sometimes the Hudson Dispatch. My father stillreads just El Diario (a Spanish language paper) because he doesn't speak enough English."

He smiled. "Someday," he said, "I'll get him to start reading The Times."