The Immigration and Naturalization Service has ruled that 41 Cubans who arrived here last month to seek political asylum must be deported as part of a new crackdown on illegal aliens.

Kept in confinement since they arrived from Spain on March 21, without U.S. visas, the group of adults and children has become a cause celebre in Miami's 700,000-member Latin community.

In the past, the Cubans would likely have been admitted as refugees fleeing Fidel Castro's communism even if they arrived from a country other than Cuba. But now INS authorities say immigration policies will be applied equally, even to Cubans who have enjoyed a privileged immigration status for 22 years.

"It is an effort to truly enforce INS law equally," said INS district director Joe Howerton.

The only way the 41 Cubans can remain in the United States is to win political asylum. But the State Department has rejected that request, saying they have no "well-founded fear of persecution," the grounds for asylum, should they return to Spain.

The decision has bewildered the Cubans. "We came here because we've always seen the U.S. accept people with open arms," said Olga Cepero as she sat in a guarded refugee camp 25 miles outside Miami.

Acting INS commissioner David Crosland ordered on Feb. 23 that all illegal aliens who arrive at U.S. airports with fake visas or no immigration papers should be detained and referred for deportation.

This directive and recently resumed efforts to deport 5,000 Haitian "boat people" who have arrived since last fall are aimed at stopping what appears to be a surging new spring flood of refugees into Florida.

Just one year ago, the "Freedom Flotilla" boatlift from Mariel Harbor in Cuba began, bringing 125,000 refugees by September.

"What the government is working toward is not allowing the situation to get worse and not to permit a second Mariel," said Larry Mahoney of the Cuban-Haitian Task Force in Miami.

More than 100 illegal aliens arriving at airports, mainly in Miami, have been caught in the changing government winds.

"This is absurd," said Angel Blanco, a Miamian who is related to some of the 41 Cubans. "They are not going to become a public burden. The families have set up bank accounts for them. We would take care of our own."

Cepero, one of the 41, says, "Now we are afraid. The children cry a lot. One boy asks his mother why is he in 'prison.' We can't see our husbands, our other children, our American relatives. We're afraid to move around in here."

The women and children sit on aluminum cots covered with Army blankets in a large drab, concrete-block room. A doll, jigsaw puzzle, crayons and a beach ball are scattered about. Within hearing distance, about 600 Haitian refugees mill around.

The Cubans speak nothing but Spanish. They trust no one. Cepero finally consented to sign a waiver to speak with a reporter after learning reporters had to sign the same paper.

"We wanted to live on our own . . . in the United States . . . to live free," she said.

The 41 Cubans flew in from Madrid. They had lived in Spain 11 months after fleeing Havana, where they were among the 10,000 asylum-seekers at the Peruvian embassy last April.

In Spain, life was hard. They say they were not welcome, they were harassed and they could not find permanent work. To augment resettlement aid from the Spanish Red Cross, they did housecleaning, dishwashing and sent their children to vend popcorn and candy on the streets. The initial $200 a month from the Red Cross was eventually cut to $120. This month it would have run out.

One day Cepero's husband saw a travel poster for Mexico. Rather than waiting months, possibly years, for visas to the United States, the Ceperos and three other families decided to leave. The airfare was sent by U.S. relatives. They obtained tourist visas to Mexico at the airport. They left the plane in Miami during a refueling stop.

"Hey, Francisco, it's Enrico!" one of the 41 told his cousin Francisco Caballero in a telephone call on his arrival in Miami. Caballero, a former Cuban refuge who is now an American citizen, said he was surprised.

Instead of rejoicing with their relatives, however, the Cubans were put in a Miami airport motel under Aeromexico security. The INS procedures require an airline to detain illegal aliens while the government decides what to do with them and eventually return them to where they came from, if necessary. Aeromexico received a $12,000 bill from the motel for rooms and meals and faces a $1,000 fine for each illegal Cuban brought in.

After nine days, the INS took custody and dispersed the Cubans to three refugee centers: the women and four children to one, the adult men to the Federal Correctional Institute and three teen-age boys to a youth hall in West Palm Beach 60 miles north.

While their appeals are pending, they sit. The immigration court hearings began last week, and the first of the 41 who went to trial were denied asylum but said they would appeal.

Soon after he was confined, Julio Blanco, 14, called Caballero in tears. "He wanted me to visit him," Caballero said. "He said he was alone with the two other boys in a room with a female correctional officer who didn't speak Spanish. He didn't know where his parents were."

"I don't understand English," said the boy through an interpreter. "I can't talk to anyone."