A new under current is running in the streets and alleys of this city's "Little Havana," so often riddled with murder, bombings and fear in recent years.

It is an undercurrent not of violence, but of reconciliation. It's based not on fear, but on a growing acceptance - particularly among the young - of the permanence of the Castro government plus the very human desire of many Cuban exiles to visit the relatives and friends they left behing when they fled.

The shift is still largely unspoken.

"People are afraid. Everyone is afraid to say anything," said Angle Morera, who works for a firm that arranges visits to the United States by Cubans. "They're afraid someone will go boom, boom, boom."

The fears are very real as the Carter administration moves toward re-establishing relationships with Cuba. When Mackey International Airlines announced plans to begin the first regularly scheduled flights to Cuba since 1961, its headquarters were bombed. When Carras Cruise Lines began sailing to Havana, it received a series of threats, and this week it canceled bookings for June. And both law enforcement officials and anti-castro leaders predict more wavs of terror.

"There's no way you can control it. We're at war," Roberto Carballo, president of Brigada 2506, the Bay of Pigs Veteran group, said solemnly.

But this kind of statement tends to overshadow a more important - and largely ignored - movement in this city's huge Cuban community: a dramatic shift in the exiles' long-held opposition to normalizing relations.

The most compelling evidence is a poll of 321 exiles conducted in March by Dr. Juan Clark, a sociologist and Bay of Pigs veteran. It found heads of households split almost evenly (36.5 per cent against and 35.9 per cent for) over the question of normal relations.

Clark, a professor at Dade County Community College and an anti-Castroite, said much of the shift has taken place since 1975, when he conducted a similar study. He said a large number of those surveyed have since become U.S. citizens, developing roots in this country, and regardless of the outcome of the Castro government only a small fraction of them would want to return."

After 18 years, much of the emotion has drained from the issue, here "Cubans have been conditioned by so many broken promises that we don't react anymore," said Alberto R. Gardenas, a young attorney who was Spanish campaign chairman for Ronald Reagan last year. "We're not as emotional a group as we're characterized as. We're a sophisticated community. We drink gin and tonic, play tennis and watch TV like everyone else."

The Cuban community, which now claims more than a third of Miami's population, remains vehemently anti-Castro and anti-Communist. A small but well organized and trained - initially by the CIA - corps of militant anti-Castroites continues to operate, often associated with terrorist activities.

Few established community leaders are willing to challenge them, or their activities. None has publicly advocated normalizing relations.

That would be a very, difficult thing to do," said Alfredo Duran, prominent lawyer and state Democratic Party leader. "It would take a tremendous amount of courage."

It is hard to overstate the fear in the community. When Luciana Nieves advocated peaceful coexistence with the Castro regime he was assassinated in February, 1975. When Emilio Milian, a local broadcaster, criticized terrorism on WQBA, a Spanish station, his car was bombed. His legs were blown off, just below the knees. A guard, armed with a machine gun, now stays near his side.

"I don't like terriorism, no matter if it's on the left or right," he said this week. "They wanted to kill me because I was independent."

The signs of reconciliation are less obvious, often stated guardedly. Frequently they have more to do with human need than politics. Said a 50-year old woman, for example, in her yard in Hialeah: "I feel happy about normalizing relations. We could travel there and they could travel here. ,My mother and brother are still over there. I'd like to see them. But don't tell anyone I said that."

Still there are concrete - if seemingly minor - signs of a real undercurrent of change. Most are unnoticed. Every other week now, for example, about 20 Cuban nationals arrive in Miami, by way of either Mexico City or jamaica, to visit relatives for two or three months.

When Almacen el Espanol, the firm that arranges these flights, started business two years ago its headquarters were bombed twice. But it hasn't had any trouble since. "Yes, at the beginning we were afraid of threats. But people have realized this isn't political," said owner Alberto Rodriques. "It doesn't matter what you think about Castro. It's a private thing among families."

The visitors are mostly older Cubans, separated from their families as long as 18 years. For the last two years, the Castro government has, unknown to most Americans, allowed a limited number of them to visit the United States and then return. (Formerly, Cubans who fled were not allowed to return.) Applications from technical workers and those of military age are not considered.

According to Rodriques, about 900 persons have done this.

They come sparsley clad and leave with 10 to 20 suitcases full of clothing, electrical appliances, medicine and spices, all of which are in short supply in Cuba.

In interviews, they shy from politics, but speak wondrously of how well their children and friends have done in America. "You can't compare here with Cuba," said Juana Lorenzo, 60. "There you lack everything. You go to a department store and find nothing. Here you have everything."

The Cubans have found their grandchildren largely Americanized, often speaking a mix of Spanish and English, called "Splangish," which the visitors find unintelligible.

Often the youngsters know little of Cuba. Of six sophomores and juniors interviewed randomly at Miami High School, which has an 85 per cent Latin enrollment, only two could identify the Bay of Pigs. "I think we read about it in history," one said. "Wasn't it an air base or something somewhere?"

Recent months have also seen the emergence of a new spokesperson for coexistence with the Castro regime. Christina Marie Herrarah, a professor at Dade County Community College, wrote a strongly worded letter to the Miami Herald: "It is high time to speak out an say that bombthrowers and slanderers are only a sick and alienated minority" abhorred by most Cubans.

She blamed much of the trouble in the Cuban community on CIA-trained agents, noting that in the early 1960s "being a CIA agent was a (way) to secure a livelihood and to fight for Cuba's freedom."

Once trained in subversive activities and violence, these CIA-trained agents had to find a way to channel their "habits of violence," so some turned to organized crime and narcotics traffic, she alleged in an interview. tr add ten

If these charges weren't enough to stir emotions, Herrarah appeared on a local television program with other Cubans discussing Carter administration moves to ease hostilities with Cuba, and she advocated full diplomatic recognition of the Castro regime. She said, "There were some people who told me I incurred great risk in doing . . . My impression is that a lot of people feel the way I do, but they don't find it convenient to say so."