The first lady of the Republic of Nicaragua likes to walk aimlessly in the marketplace, talk with her mouth full, forget what time it is and be half crazy. She also likes the president of Nicaragua -- particularly his hair, his eyes and his "hands, always occupied with many large and important matters." Every so often she has an urge "to invent a perfectly incredible story" to make everyone laugh, even when she herself feels like crying -- "like a sad, frightened rabbit."

It's all there in her latest book of poetry, hot off the presses from Editorial Nueva Nicaragua, the state-run publishing house.

"What I don't like is having the ceremony," says Rosario Murillo, who is not only the better half of Nicaraguan President Daniel Ortega, but also the author of five volumes of blank verse, the secretary general of the Sandinista Cultural Workers Association, the secretary general of the Nicaraguan Writer's Union, a delegate to her country's national assembly as well as to the Sandinista assembly and the editor of Ventana ("window"), the weekly cultural supplement to Barricada ("barricade"), the official party newspaper.

Oh yes -- she's a mother of seven. And she's 34.

"The worst thing is protocol for me. I don't like it," she says in lilting English, her continental accent picked up in a British convent school and a Swiss finishing school. "For instance, if I want to come barefoot from my room, why do I have to wear shoes? Only because I am the first lady. What's security going to say if you don't wear shoes?"

Indeed, her hatred of protocol might be called revolutionary, at least among the world's first couples.

"Daniel and I have a common-law marriage," she says of the man in her life and the leader of her nation. "We didn't have a ceremony. We don't have a religious marriage. You know, this is a common situation in Nicaragua. Most of the peasants, for example. They never got married. Most of the workers, they never got married. They just live together. So the Nicaraguan people don't worry about that."

"She's young, she's attractive, she does her homework, she knows the line and she says it in English," says a State Department spokesman. "She's a skilled propagandist. Just like Gorbachev, she puts a good face on for the public."

She is raven-haired, with huge brown eyes and an air of deep mystery -- the latter enhanced whenever she recounts her adventures in the revolutionary underground that toppled Anastasio Somoza. She tells stories of transporting weapons in her car, harboring companeros in her house, being followed day and night by Somoza's security police and spending 12 days in 1975 under arrest with a pillowcase over her head; of revolutionary martyrs, poets and peasants who, "by themselves, against a hundred of the National Guard, refused to surrender, 'Tu madre!,' they said -- and they died singing the national anthem."

All her tales lead to July 1979, the month of what is now called, simply, "The Triumph."

"We used to call ourselves by different names," she says. "Pseudonyms -- is that the word? Daniel's was 'Enrique.' I had lots of them. The first one I had was 'Carolina.' Then I was called 'Ernestina.' Then I was called 'Gabriella.' Then I was called 'Amparo.' It means 'shelter.' " She giggles. "I didn't think of that at the time. Then I picked up a name from a story by Poe. 'Berenice Valdemar.' I loved that name."

Her delicately wrought hands are covered with rings, and she sports the sort of chic knit ("I never notice what kind of dresses I'm wearing -- I just get them from friends," she says) that Nancy Reagan might easily slip into. Across the avenue from the United Nations, 34 floors above the limo-glutted street, she sits demurely in one of a block of elegant hotel rooms occupied by the Nicaraguan delegation.

"I don't know how to use a gun," she says. "When I proposed that I should have military training, I remember Commandante [Tomas] Borge [now Nicaragua's interior minister] told me, 'Everybody has something to do in the struggle. Not all the persons have to do all the things. You can do something with your poetry, with your writing.' In 1974 I founded a cultural movement, called 'Gradas' ['steps'], which was very important in political terms, because it was massive. We had 'happenings' with 5,000 people, 6,000 people, and painting, singing, poetry. This effort was much valued in the struggle, because it made it known to everybody that art can be a weapon of the people.

"After the victory I was trained to use, not a gun, but the rifle that the militia uses. It's very old and heavy, and I'm not very strong with my hands."

Murillo -- who assumed the job of Nicaragua's first lady last November, when Ortega ascended to the presidency in what the Sandinistas insist was a democratic election -- is clearly becoming something of a weapon herself.

This week, while the U.N. celebrated its 40th anniversary and Ortega made a speech to the general assembly, she has taken on a very public role in the Sandinistas' effort to turn American public opinion against the Reagan administration.

In interviews, on television and in receiving lines, she has been at least as visible as President Ortega -- a charismatic counterpoint to her mate's sometimes dour public image. She has defended Ortega's recent decree of a "state of emergency" curtailing civil liberties in Nicaragua as a necessary measure in a state of war. She has dismissed President Reagan's claim that her Soviet-supported country is exporting Marxist revolution, and has decried U.S. aid to the "contras," who have been waging a guerrilla operation against the Sandinistas since 1982.

On Monday she took her cause directly to Nancy Reagan, telling the American first lady at a drug-abuse forum that she hoped the two nations would have better relations one day. "I found her very warm," Murillo said later. On Tuesday, she accompanied Ortega to the "Donahue" show, where she spoke up often and, unlike her companero, got applause.

Yesterday she slammed Reagan's U.N. speech -- in which he mentioned Nicaragua as a bone of contention between the United States and the Soviet Union -- as "a reaffirmation of a continued policy of war." Today she will participate in a "town meeting" for New York supporters before flying home tomorrow.

She was born in 1951 into Nicaragua's upper middle class -- her father the owner of a cotton plantation among other ventures -- and grew up in the same Managua neighborhood as Daniel Ortega, although she didn't know him then. Murillo says her mother was a niece of the legendary anti-Somocista Augusto Sandino and that her parents quietly opposed the iron rule of the Somoza family.

Her life story from childhood on, as she tells it, could easily serve as the book for a Broadway musical -- perhaps titled "Rosario," and featuring a show-stopping song, "Don't Cry for Me, Nicaragua."

Her parents sent her away from home at age 11 for a European education, and when she returned to Nicaragua at age 15, she promptly wed the 20-year-old son of a neighboring plantation owner, bearing two children in as many years before the marriage collapsed. "I was too young," she says. "I don't know why I married. I guess because I got in love."

Joining the anti-Somoza newspaper La Prensa at age 16 as an aide to the editor, Joaquin Chamarro (who was assassinated by Somocistas in 1978), she says, she went on to have another child, then five more children by Daniel Ortega. Her third child, a boy named Joaquin, was killed in the catastrophic Nicaraguan earthquake of 1972. Six boys and a girl remain, ranging from teen-agers to infants. Baby Joaquin's death opened the floodgates of Murillo's poetry.

"This was a terrible shock," Murillo says, her eyes watering. "So I started to write, and to keep the poems I wrote." She published her first book in 1974.

In the meantime, she says, she refused her father's offer of a new house in a good neighborhood -- "He was furious, because he had to lose the down payment, but I didn't ask him to give me the money." Then she won $15,000 in the Nicaraguan national lottery.

Her winnings enabled her to build her own house and buy a Ford Cortina besides, she says. The house and the car quickly became instruments of the underground, which Murillo had joined in 1969, going on to earn a reputation as a skillful rhetoritician.

Ortega had been imprisoned in 1967 for taking part in a bank robbery in which a guard was killed -- "It was a political act to get funds for the Sandinista Front," Murillo says. The two began corresponding in the mid-'70s, he writing her letters and poems from prison. They finally met in 1976 -- after he was freed in a Sandinista-Somocista hostage exchange -- and they took up housekeeping together in exile, in various parts of Latin America.

In the nine years since, especially after her triumphant return with Ortega in 1979, she has become a person of wide influence and high position in her country. "But this has nothing to do with my role as the wife of Daniel Ortega," she says with some heat. "This is something I earned from my own background and my own work."

Murillo has been to the United States before -- notably a December 1983 visit to southern California. She stayed with patrons in Beverly Hills, speaking to gatherings that included Jane Fonda, Warren Beatty and Sen. Gary Hart (D-Colo.), spreading her message over canape's and cocktails.

That occasion may have had some of the surreal overtones that this one does, as she sits in a decidedly unrevolutionary overstuffed chair, talking about her war-torn country of 3.5 million -- between visits with Bianca Jagger, Harry Belafonte and various heads of state.

"It's very difficult to be a woman in Nicaragua right now -- a normal housewife, a mother," the first lady says. "Apart from being scared of losing a child or losing a husband, we come to the market every day and we're not finding what we need. One week it might be rice, another week it might be beans or cooking oil or soap, but you know, of course you get mad.

"But then, me, myself, if I can't find, rice, let's say, one week, I say 'Oh my God, what are we going to eat?' You find potatoes or something else, and you get mad, but then you start thinking, and you realize that this is because we are at war."

If the first family does suffer such shortages, they would be well outside the norm among Nicaragua's privileged leadership, known for living in well-guarded houses in Managua's best neighborhood and shopping at restricted "dollar" stores.

But Nicaragua is worlds away from midtown Manhattan. And what appears obvious to some is often open to dispute.

Asked about published reports of book burnings after the Sandinistas came to power, Murillo seems surprised.

"Burning of books? That never happened, I'm sorry. We are in such need of books. We never burned books." Turning to a note-taking aide, she asks, "Have you ever heard that?"

"There are some books," the aide says, "which are totally inappropriate." If books were burned, Murillo adds, "That's personal initiative. Someone comes and says, 'I want to burn all this,' you can't stop them."

Asked about censorship of the press, she says, "The government has to control it some, especially military information. There have been some excesses and we have said that. We can't be perfect."

Persecution of the Catholic Church?

"How could we do it? My mother-in-law is a Catholic and she prays every day. Our people are Catholic . . . It isn't a problem with the church or with religion. It's a matter of some church representatives who want to interfere, to influence in politics." The pope, for example, who has strongly criticized the Sandinistas? "Unfortunately, the holy father doesn't get the right information about what's happening in Nicaragua."

Asked about reports that Nicaraguan schoolchildren learn math from textbooks that feature illustrations of grenades, she deftly turns the question around.

"I've never seen that. Supposing that's true, I don't know, what is worse for children, I wonder? Learning how to count with those images, or to have to go and practice every week how to hide in trenches because we can have an air attack coming from the U.S. if there is an intervention any time? What is worse, learning how to count with those figures or to be constantly scared of losing your father, losing your mother, of seeing the school that you attend destroyed? I wonder what's worse."

In the midst of all these troubles, Murillo worries about wasting time on the "delicate word," as she writes in one of her poems, when more pressing matters loom.

"To whom is a delicate word important, when compared with the macro-cosmos and the precise figures of the macro-economy, the macro-geography, the macro-vision . . .

"I, a simple woman with a million defects . . . "