Cornelio (Nelo) Bravo has spent most of his 72 years on horseback, a real-life Marlboro man riding the rugged hills of his ranches and tending herds of cattle as they fattened on the sweet natural grass of Nicaragua.

Bravo has had some rough moments all right, like the time about 30 years ago when a horse fell and crushed his leg. He still limps from that, and probably will into the grave. But to hear him tell his story over rum and water, it mostly has been a perfect marriage between a cowboy and his land.

"I was raised with cattle," Bravo said recently to a visitor at his daughter's home here, "and that's what I've done all my life. It was horseback day and night. That was my happy life."

Nicaragua has many men like Bravo. Some raise cattle as he does, turning out delicious cuts in a region famous for steaks, and making meat the fourth-largest export.

Others have different jobs. But they all seem to share in the tradition of individualism, personal independence and cowboy bravura that has marked Nicaragua for generations and still helps explain a lot of what goes on here, six years into a Marxist-led revolution.

Men like Bravo say the Sandinista government, so hotly disputed in Washington, matters little to them if they are allowed to raise their cattle as they always have. "As long as they leave me alone, I don't care who's in charge," Bravo declared.

But, perhaps inevitably, many ranchers are not being left alone. Some land has been confiscated since the Sandinista takeover in 1979 and ranchers fear more is certain to follow, perhaps threatening their livelihood and even their way of life.

Moreover, with the Sandinista desire to reorganize society and anti-Sandinista guerrilla attacks raising security concerns, the freedom symbolized by cowboys in fiction and real life has been curtailed. A foreigner trying to visit Bravo's ranches in Chontales province recently, for example, was turned back on the main highway from Managua by Interior Ministry police, who called the area "a war zone."

It is not surprising then that some have responded by joining the anti-Sandinista forces. It is an interesting turn of fate for some of the leaders of the Sandinista revolution, whose own roots go back to ranching communities.

President Daniel Ortega, denounced by President Reagan as a "dictator in designer glasses," actually comes from a one-horse town called La Libertad that lies near Bravo's ranchlands in the cattle country known by many as the Texas of Nicaragua.

Ortega, who has denounced Reagan for "cowboy" conduct of U.S. foreign policy, thus grew up close to Bravo and the other cowboys. Conscious of the tradition, he made appearances on a white stallion during the 1984 election campaign. For many, the prickly nationalism of his ruling Sandinista National Liberation Front also has some of its roots in frontier-style refusal to take U.S. orders.

Another son of La Libertad who went on to bigger but different things is Cardinal Miguel Obando y Bravo. The most prominent critic of Nicaragua's Sandinista rulers, he has stubbornly refused to bend what he sees as the interests of church hierarchy in order to get along with the revolution.

Obando operates from a platform strengthened by the affection of thousands of Nicaraguans who have recognized their traditions in him. As a young priest, true to his heritage, he traveled alone from village to village on muleback to carry his ministry to the isolated areas that other clerics rarely visited.

The importance of such tradition was driven home to another Nicaraguan prelate, Bishop Pablo Antonio Vega, soon after he arrived to take over a diocese headquartered in Juigalpa, the main town in Chontales. At first coolly received by his flock in visits to villages, he recalls that things changed dramatically when, on advice from a local resident, he parked his jeep and rode the circuit on horse.

Eden Pastora, a Wild West figure who became famous as "Commander Zero" during the Sandinistas' 1978 takeover of the National Palace in Managua, likes to tell visitors of his own roots on a cattle farm in the central mountains.

Pastora, who now seeks to fight against Sandinista rule with a new set of guerrillas, recalls that ideology had little to do with his original decision to join the Sandinista underground in the 1970s. Instead, he accuses president Anastasio Somoza of having Pastora's father killed during a land feud of the kind that provided the plot for many a western movie in the United States.

The original Sandinista and now Nicargua's national hero who fought U.S. Marines here in the 1920s, Augusto Cesar Sandino, also is remembered as a cowboy warrior, vaguely resembling Tom Mix. He nearly always is pictured in a cowboy hat distinctly larger than 10 gallons, tipped at a jaunty angle, with a six-shooter on his hip.

According to Sandinista historians, the image accurately reflected a cocky man worthy of cowboy traditions. When, in 1927, U.S. Marine captain Gilbert Hatfield demanded by telegram that Sandino and his men surrender or face attack, the Nicaraguan rebel wired back from his mountain hideout:

"Received your communication yesterday and I understand it. I will not surrender and I await you here. I want a free fatherland or death. I do not fear you. I count on the ardor of the patriotism of those who accompany me."

Billboards with the text of Sandino's defiant message have been erected in Managua near Ortega's offices and across from the entrance to the U.S. Embassy.

With his U.S. cowboy tradition to defend, Hatfield was not to be outdone. On another occasion, he responded to a taunt from Sandino with a telegram of his own: "If words were bullets and phrases were soldiers, you would be a field marshal instead of a mule thief."

Some of the same type of mountain individualists who followed Sandino against the U.S. Marines are now following U.S.-sponsored rebel leaders. Youths interviewed in rebel camps repeatedly explain their decision to join the insurgents by citing instances of zealous Sandinista officials interfering with traditional family farms.

At least until recently, combatants from the main rebel organization, the Nicaraguan Democratic Force, have been marauding through the Chontales cattle country. Ranchers say they steal cattle for food and occasionally press ranch hands into their bands.

True to tradition, the ranchers say, the rebels have been showing up on horses, riding instead of marching into the sunset.