HIS DARK eyes flash fire, and when he speaks of "the Spanish" he means the conquistadores. His hatred is as fierce as if they had come yesterday, but his sense of human dignity is ageless.

Juan Binilla Aguirre, professor of Indian history and English language at the Oaxaca Normal School, stands before a group of tourists at Mitla, the ruins of the one-time Mixtec cemetery where intricate mosaics still defyarcheologists' efforts to decipher their meaning.

Mitla is one of several major sidetrips out of Oaxaca, the Zapotec-Colonial state capital that gave the country some of its most famous native sons -- Benito Juarez, the Zapotec shepherd educated by the Church in the early 19th century who ultimately became the country's chief revolutionary leader, and Porfirio Diaz, who reworked the revolution to his own design in the early 1900s.

"The Spanish conquest," Professor Aguirre is saying, "was not made so much by fighting as by stepping on people's feelings. They took the stones from the ancient tombs to build the cathedral . . ." This was as true in Mitla, only a few miles from the city of Oaxaca, as it was in Mexico City some 300 hundred miles to the north.

In fact, says Aguirre, "I am half-Spanish myself. My last name is Aguirre, but my mother is Zapotec."

He is not tall -- about 5-feet-7 -- but he believes that his Zapotec ancestors were much larger men. (He speculates that generations of oppression have physically diminished his race.) His high cheekbones and slanty eyes betoken his Zapotec forbears and his pride in his Indian ancestry is almost tangible as he stands in the broiling sun, trying to communicate his own sense of the past to a group of hot and restive tourists, many of whom have difficulty understanding him.

Not that his English isn't excellent. But the so-called "English" tour is a polyglot of everybody who doesn't speak Spanish. This includes a charming Swiss couple of honeymooners (he speaks French and understands a bit of English, she speaks only a Swiss canton dialect) and a German couple who try to hire Aguirre to drive them to the airport later that day. The professor puts them off politely, but his eyes narrow . . .

Today's Zapotecs, more or less pure blooded, live in the hilly but fertile environs, peddling produce, cheese, cactus-based alcoholic drinks and Oaxaca's famous black pottery to city dwellers and an increasing number of tourists who are drawn to this still unspoiled, mostly non-touristy and very charming city. The guidebooks encourage tourists to bargain, but given the relative ratio of dollar to peso, conscience may dictate a less than vigorous bargaining posture on the part of the American buyer. You are, said one recent tourist, "probably bargaining away somebody's kid's dinner."

The Oaxaca city museum attached to the impressive fortress-cathedral sports an extraordinary treasure recovered from the nearby Mixtec-Zapotec sites, mostly within the last half-century.

And the noted Mexican artist Rufino Tamayo, a native of Oaxaca, left his own impressive collection of pre-Columbian art works to the city, which are displayed in the Tamayo Museum.

Near the city is the 3,000-year-old tree of Tule, awesome enough with its 135-foot circumference and home to thousands of noisy birds. It is, alas, dying, of what plant pathologists do not know, nor can they seem to halt the slow progress of decay. "Three thousand years," says a guide with a shrug, "is long enough . . ."

But perhaps the major nearby ruin is Monte Alban, where the mysterious but sophisticated and civilized Olmecs have left remnants as old as the Tree of Tule, and where later the warlike Zapotecs played a deadly ball game in which the victor's reward was to have his heart cut out -- to the glory of the gods.

In its most recent history Monte Alban was used as a burial site, and only 40 years ago a tomb was uncovered filled with treasure: gold, pearls, onyx, corals, turquoise jewels and implements, all on display in Oaxaca.

But the farther back the ruins go, the more fascinating they become. There are, for example, the pyramids and walls built of such extraordinarily carved stone, fit together with such mathematical precision, that by giving a little here and then sliding against each other a little there they have withstood more than 2,000 years of volcanic rumblings and earthquakes. Not that they look all that symmetrical. But they are earthquake proof as nothing built today can even approach.

Then there are the steles, the huge carved slabs. There is the one called "the Chinaman," and there is nothing abstract about it. It is a carving of a Chinese personage of some 2,500 years ago. His facial characteristics and the long pigtail down his back are unmistakable. He is only one hint of ancient Asian influence in Central America -- another, of course, is the physiognomy and coloring of the Zapotecs themselves. It is titillating, intriguing and, ultimately, perplexing -- who they were, how they got there and why.

Just as fascinating are the so-called dancers' steles in the "Temple of the Dancers." The archeologists who discovered the treasures of Monte Alban described a group of carved slabs as representational of dancing figures.

Subsequent analyses have shown them much more likely to be figures of people undergoing surgical procedures or even women in labor. One stele is clearly a representation of a pregnant woman in the throes of a breech birth -- the baby is being born feet first. Another indicates a kind of brain surgery. Monte Alban, at some long past date, apparently was a medical school, and a pretty sophisticated one at that.

There are no active archeological digs in the Mitla-Monte Alban region at this time, "a tragedy" the guides are quick to tell you. They direct attention over the mountains pointing to gentle, rolling mounds on mountain sides and tops.

"Every one of those hides a temple, a tomb, a key to our most ancient past," says Aguirre. He speaks with longing and, for a moment, he seems very far away.