On the sacred walls and inside the dark passageways of ancient ruins in Guatemala, archaeologists are making discoveries that open expanded vistas of the vibrant Maya civilization in its formative period, a time reaching back more than 1,000 years before its celebrated Classic epoch.

The intriguing finds, including art masterpieces and the earliest known Maya writing, are overturning old ideas of the Preclassic period. It was not a kind of dark age, as once thought, of a culture that emerged and bloomed in Classic times, at places like the spectacular royal ruin at Pelanque beginning about A.D. 250 and extending to its mysterious collapse around 900.

At the derelict ceremonial center of pyramids and wide plazas, a site in remote northeastern Guatemala known as San Bartolo, archaeologists have uncovered the unexpected remains of murals in vivid colors depicting the Maya mythology of creation and kingship.

The murals date to 100 B.C., and nearby, a column of hieroglyphs, a century or two older, attests to an already well-developed writing system.

News of the discoveries, announced in the last six months by an American-Guatemalan team led by Dr. William A. Saturno of the University of New Hampshire, is reverberating through the small community of Mayanists.

They see these and other recent finds as strong evidence for the early origin and remarkable continuity of the culture's concepts of cosmology and possibly governance over more than a Preclassic millennium.

The Classic splendor was no sudden, unanticipated efflorescence.

Coming away from a visit to San Bartolo, Dr. Michael D. Coe, a retired Yale Mayanist who was not involved in the work, called the murals "one of the greatest Maya discoveries of all time."

Dr. Stephen Houston, of Brown, said, "We are entering a golden age of Preclassic study," adding that the discipline of Maya research "will be marked by a time before the discovery of these paintings in the jungle of Guatemala, and a time thereafter." Other experts have already focused new research on Preclassic ruins, some dating at least to 900 B.C., and are reinterpreting finds in light of the San Bartolo evidence.

"San Bartolo has created excitement and momentum for investigations deeper into the Preclassic period," said Dr. Julia Guernsey, a specialist in art history and Maya iconography at the University of Texas. "More attention is being paid to the antecedents of the Classic Maya."

In her book "Ritual and Power in Stone," to be published in December, Guernsey reviews many examples of stucco facades, painted murals and carved monuments that illustrate Preclassic development of the imagery of enduring Maya concepts of creation, the spirit world and the metaphorical expression of power and authority of rulers.

New attention, Guernsey said, is centered on the common monumental motif in the Classic period that has now been increasingly recognized as early as the middle Preclassic era, 900 to 300 B.C. It is known as the quatrefoil. The design is something like a four-leaf clover and is found in the arrangement of stones or carved in stone or crated with packed earth and painted clay at a ceremonial site, as at La Blanca on the Pacific coastal plain in Guatemala. La Blanca, occupied from 900 B.C. to 600 B.C., is being excavated by Michael W. Love of California State University-Northridge, with Guernsey as the project iconographer.

Other Preclassic examples are being examined at Izapa, across the Mexican border from La Blanca, where quatrefoils and monuments date to between 300 B.C. and 50 B.C. An Izapa throne is framed in a quatrefoil. Similar imagery has been uncovered in Mexico at Chalcatzingo, dating from as early as 700 B.C. Guernsey said this was "the clearest expression of the links between quatrefoils, animal mouths, caves and portals."

Archaeologists think the quatrefoil, often in association with water channels and basins, may have been part of the iconography in ceremonies to the rain god and fertility. In other cases, it is formed around a cave entrance, perhaps symbolic of creation and the supernatural.

Guernsey surmised that the previously underappreciated quatrefoil might have been a prop for public performances in which the ruler dances and passes through the open center in a ritual demonstrating his power to intercede with the gods, hence his authority as leader. Even then, rulers were actors, and this was the Maya version of a staged photo opportunity.

Today, the quatrefoil can be seen as a symbolic portal through which archaeologists are passing to explore mysteries of Maya culture far back in Preclassic time.

One new puzzle yet to be solved is the Preclassic Maya script found at San Bartolo. The column of 10 glyphs, painted in black on white plaster, is definitely Maya writing from 300 B.C. to 200 B.C., experts say, but so far it is unreadable.

Saturno, the discoverer, and colleagues reported that the writing sample "implies that a developed Maya writing system was in use centuries earlier than previously thought, approximating a time when we see the earliest scripts elsewhere in Mesoamerica."

Houston, an expert, at Brown, in Maya glyphs, agrees, saying the sophistication of the scribe's technique and the inventory of signs suggest that "this was not a system invented the day before." How long before, a few generations or centuries, he added, is not known in the absence of further evidence, but its origins could be contemporaneous with Zapotec writing in Oaxaca, Mexico, or some symbolic systems of the Olmec along the Gulf Coast.

The origin of writing in Mesoamerica, the area of southern Mexico and parts of Central America, is a contentious issue. Zapotec scholars say writing started first in Oaxaca as early as 600 B.C. and spread into Maya territory to the south. But if it did, the San Bartolo glyphs show the time gap is closing.

At the University of Texas, Dr. David Stuart, a professor of Mesoamerican art and writing, ran his finger down a drawing of the San Bartolo text. Such Maya glyphs are stylized lines and dots with animate figures, some human and others birds, snake heads and jaguars. It is writing with an alphabet, and had defied decipherment until the last decades of the 20th century.

"The text is 1,000 years before the late Classic writing, which we are good at reading — up to 95 percent of it," Stuart said. "Any script is going to go through significant changes over that time. But these glyphs are very unusual, very different from later writing."

The single glyph he thought he could read was the seventh one down the column. It includes the sign for the word lord or noble. "But if it referred to a true king," Stuart said, "the sign would have a symbol with it to say 'divine lord.'"

A hand appears to be in the top glyph. Houston speculated that it looked like a human hand clutching a brush, perhaps referring to the scribe. Stuart pointed to what could be a human profile in the 9th glyph, a bird perched on a nest in the 8th one and a bird with hooked beak in the 10th. But neither expert could say what the message was.

This inability to read the text, Houston said, may be because the Maya system underwent a major change at the time the Preclassic culture collapsed, around A.D. 100 to 200, with widespread evidence of destroyed or abandoned cities.

Even though the disruption was sharp, scholars say, the similarities between the few samples of Preclassic writing and the Classic style testify to a measure of continuity. But it was not as obvious, say, as the transitions from Chaucerian English to Shakespeare down to that used on blogs.

As in any code breaking, Stuart said, success usually depends on having many text samples to work with. Even computers would not speed up decipherment. "Computers would be overwhelmed by the virtual variations," he said. "There's a human element to it. A computer code breaker would be fabled, and the human mind is the only thing that can access this, because the glyphs were created by humans."

Archaeologists expressed hope that more of the text or similar ones would eventually be found and that new efforts would be made to search for writing at larger Preclassic sites, like the ruins around El Mirador.

The 100 B.C. murals at San Bartolo, one 30 feet long, were found in a pyramid chamber below 50 feet of rubble. Saturno found the first painting when he ducked into a trench for shade and saw the face of a maize god on the north wall. It took two years of careful digging to expose the entire chamber.

Examining the painting on the west wall, scholars recognized figures and mythic scenes common to much later Maya art. It was the traditional Maya depiction of creation as it has been described in manuscripts some 13 centuries later. The world is supported by trees with roots running into the underworld and branches hold the sky. The trees represent the four corners of the world and water, earth, sky and paradise.

In the mural, the maize god is setting up the tree at the center of the world and crowning himself king. Scenes depict the god's birth, death and resurrection. Other deities make blood sacrifices at each tree.

"Art speaks volumes, and we don't necessarily need the texts," said Guernsey, the art historian.

The San Bartolo art provided Dr. David Freidel, an archaeologist at Southern Methodist University, with insights for interpreting a discovery his team made earlier at Yaxuna in the Yucatan. Members uncovered a ceremonial structure that contained a cloverleaf pattern like a quatrefoil. Beneath, they found pottery, an ax and other artifacts from the late Preclassic period but in the style of the earlier Olmec civilization.

Freidel concluded that the Maya rulers at Yaxuna held ceremonies to connect their reign to the preceding Olmec culture, which faded away in the fifth century B.C.

Other recent digs have revealed stone monuments, altars and figurines at La Naranjo, near Guatemala City, that was occupied as early as 800 B.C. Naranjo, Stuart said, "is proving to be one of the most exciting excavations in the Maya area."

The chief excavator, Barbara Arroyo of the University of San Carlos in Guatemala, said Naranjo was an important ritual site near a water spring. The origin of the gods is associated with places where water flows.

In his autobiography, "Final Report," being published this month by Thames & Hudson, Coe, the Yale Mayanist, concluded: "The great age of Maya archaeology is far from over. In fact, it's just beginning."