Cuba's official newspaper Granma, so widely quoted by the foreign press in these days of crises, has a secret contributor.

The paper, named after the yacht on which Fidel Castro's guerrillas invaded Cuba, is usually drab, full of exhortations, of work achievements in the harvest or a factory, reports of socialist officials greeting each other around the world.

But in the past month it has become alive with long, front-page editorials that do more than state the position of the Cuban government. These texts, prominently displayed in a large red box, are pointed, often witty, full of anti-American invective and written in a chatty, defiant sytle. w

They have recently called President Carter a "Pharisee" in a "whitewashed tomb," to quote from "his own Bible," and scolded the U.S. press as "one of the biggest ripoffs in history."

The author of most of these pieces reportedly is none often than Fidel Castro. During the past month, reliable sources said, Castro has showed up at very late hours at the offices of Granma, which has a 5 a.m. deadline.

The current refugee conflict "is too important to Castro for him to leave this to anyone else," said one person who knows the Cuban president well. "Besides, he is enjoying the writing as well."

Castro frequently calls unannounced on visitors well after midnight and he is said to retire shortly before dawn, sleeping through until close to noon.

HAVANA'S WESTERN embassies are small islands of prosperity that are rare affected by the Cuba's ups and downs. Broad import privileges and shopping at the "Diplo" store insulate them from scarcity.

Most diplomats have no access to key Cuban officials and so they keep a busy and elegant social life to swap bits of information among themselves.

But the vast exodus of Cubans to the United States is taking its tolls at the embassies, too. Many of their Cuban staff members, who through the embassies have been able to taste the pleasures of the outside consumers' world, are among those fleeing.

The Libyan Embassy has lost its chauffeur, the Japanese its handyman. The Venezuelans lost their gardener and a butler. "It's a real psychosis. The staff talks about nothing else and they're all egging each other on," one diplomat sighed.

The wife of a European ambassador said she was close to despair: "I've lost both my maids, I have a large dinner party on Sunday, and now my cook is packing her bags."

CUBANS HAVE GONE to great lengths to become eligible for an exit visa and a place on board the U.S.-bound boats. They stand in line for days, invent American relatives and diseases that require treatment in the United States and they put up with beatings and hostility in their neighborhood.

One family put off by the long lines outside the Havana emigration office, debated the merits of burglazing a house. They would get caught and be classified as common criminals, they reasoned, and this would be an expedient way to travel because common criminals were said to be getting out faster.

A HAVANA cigar factor in normal times is a tranquil and contemplative place to work. The mood is set by a 19th century tradition far surpassing Muzak as a work stimulus. It is known as the reader.

He is full-time employe, sitting among the workers in the large factory halls amid the perfume of hot, moist tobacco leaves that has crept into the walls and the furniture.

In the long hours when the leaves are cut and rolled, he reads in a loud voice whatever the workers vote to hear. He works his way through novels by Tolstoy, Spanish or English classics, political or economics texts, a speech by Castro.

Cigar workers may well be the literate members of Cuba's working class.

a fungus has diminished Cuba's recent tobacco crops dangerously and some cigar factories have closed. But Upmann's cigar factory was open last week, and indignation about "traitors" leaving the country was great. Eleven of Upmann's 846 workers had dropped out to go to the United States and these longtime colleagues were quickly branded as "riffraff and scum."

The reader was replaced by revolutionary pep talks, speeches about the workers' undying support the "Fidel and about the new American conspiracy against Cuba.

But in contract to the demonstrating crowds that roamed the streets here, the rows of men and women did not stop work. In their left hands they held the tobacco leaves and in their right a special rounded knife as they listened attentively. But every time a speaker would reach a new peak in revoluntionary oratory, a loud clatter range through the room. As if on cue, the cigar workers would beat a tattoo on the tables with ther knives.