In Brazil's Wild West, a man lives by his honor, one hand on gun

A cowboy rides into town, black stetson at a jaunty angle, holstered pistol at his waist, lasso looped from his saddle. His horse lopes along the dusty street lined with unpainted wooden buildings - past a general provisions store, a lawyer's office, a bar.

But no one challenges him to a shoot-out and he doesn't order a sarsaparilla or any other beverage. For this is not the beginning of a good, old-fashioned ''western'' movie - just a typical scene in rural Brazil today.

Brazil is known for its sambas and carnival, for soccer, coffee, and beaches, for the dense jungles of the Amazon and the sprawling concrete jungles of its congested, industrialized cities.

But this is still a pioneer country, where settlers are clearing virgin forest, where Indians are disputing the white man's claim to their ancestral lands, where men carry guns and sometimes take the law into their own hands.

The most literal ''far west'' territory in Brazil is the State of Rondonia, bordering Bolivia. Lured by the promise of cheap land, many families - especially from southern Brazil, where increasingly mechanized farming has made small holdings unviable and reduced the need for field-hands - are packing their belongings and ''going west'' to start fresh.

Covered wagons have given way to covered trucks or buses. In September the first paved highway to the state capital, Porto Velho, was opened, reducing the final 900 miles of the journey from a trip of up to 30 days to less than 24 hours.

But the settlements springing up along the new road still look pretty much like tropical versions of the old ''far west'' towns of 19th-century North America: Men on horseback mingle with trucks and buses. Farmers rub shoulders with prospectors panning for gold. Indians come to town to sell handicrafts.

Even the occasional stories of frontier violence have a familiar ring to them. A British TV crew interviewed settlers in Rondonia who had returned home after working their land to find three sons murdered. Indians apparently had killed them in revenge; a number of their tribe had been killed by a white trapper.

Rondonia is just one of the areas where the Wild West still exists here. Many a Brazilian country town, especially in the center of the nation, would make a perfect set for a cowboy movie. But even sophisticated urban dwellers show a ''far west'' mentality.

George Amado, probably Brazil's best-known modern novelist, wrote that the cocoa areas of Bahia State ''are barbarous lands, where banditry and death, implacable hatred and the cruelest revenge flourished . . . and with certain customs; gambling, drinking, flaunting one's courage, carrying a revolver. And with certain laws of conduct, one of the most binding of which was . . . the law that required a deceived husband to avenge his honor by killing the deceivers.''

Amado was referring to Brazilian life half a century ago, but a quick glance at the crime pages of any Brazilian newspaper today suggests that these ''laws of conduct'' have not entirely died out.

Over a two-year period in Sao Paulo, 722 men pleaded ''legitimate defense of honor'' as justification for killing their wives or girlfriends, according to a 1981 survey. Last year, a man was given a two-year suspended sentence for killing his wife; she had told him she wanted a divorce to marry someone else. And recently, during popular singer Lindomar Castilho's trial for a similar crime, some men rallied to his defense, calling for a return to the ''good old days'' of real machismo, the Latin American cult of male superiority.

Crimes of revenge and family feuds are another hangover from ''those heroic years.'' Last January, a young woman was murdered in her apartment in Rio de Janeiro after a nine-year family feud. Her father-in-law had accused her of killing her husband - his youngest son - and decreed her death. Over a period of years her father, her godfather, and a police detective assigned to protect her were all shot down in the streets of Rio. The father-in-law later died, but his sons apparently carried out the death sentence on his behalf.

Land ownership is at the root of many quarrels. Brazil's 220,000 Indians are not in the habit of attacking white settlements, but there have been some ugly incidents when settlers have encroached on Indian territory.

Near the small town of Unai, near the modern capital of Brasilia, peasant farmers recently appealed to their rural workers union for help. A local landowner had sent his hired gunmen to tear down their fences, destroy their crops, and burn down houses. Attempting to drive them away, the landowner offered his henchmen money to harm them, local farmers say.

The union president told reporters she went to protest to the police chief. But he told her, ''You want me to take on these armed guys? I'm not going to risk my life - anyway, I can only intervene if there's been a death.''