The California aqueduct passes very near this tree-shaded, desert town. The dark, blue-gray waters in the concrete channel snake along the edge of the Mojave, resembling a 30-foot-wide serpent bearing riches sucked from the rivers of northern California hundreds of miles away.

In a few months, Californians at last will have a chance to decide if the snake, one of this century's engineering wonders, will become a little fatter.

Southern California is about to lose a major portion of its Colorado River water to Arizona, so state officials want to build a peripheral canal around the river delta east of San Francisco Bay to increase the volume of water coming down the aqueduct from the north.

The beauty of the open, shining, white channel carrying water under the desert sun obscures the fact that southern California along with much of the growing Southwest, seems headed toward possibly many major water crises.

In some respects the peripheral canal already is too late, because the Arizona project that will take much of the Colorado River water will be ready in four years, while the canal willt take at least 10 years to build.

Former deputy secretary of state Warren Christopher, once more a prominent Los Angeles attorney, says water will surpress smog and gasoline shortages as this area's most critical issue for the next several years.

Water probably also constitutes the most divisive issue California has seen, one that is building to a major political war to the one that raged 20 years ago when the north-south aqueduct system was constructed.

Without either the aqueduct or the Colorado River water soon destined for Arizona, "it will be a year-to-year thing whether we have enough water," said Daivid N. Kennedy, an executive of the Metropolitan Water District, which recieves much of the aqueduct water coming into southern California.

The peripheral canal will cost $5 billion to $7 billion, and Kennedy and other canal supporters want construction to begin now so the cost will not escalate.

Economist Zach Willey of the Environmental Defense Fund in Berkely, one of the organization leading opposition to the canal, focuses on the costly and lengthy construction.

"There are other ways to deliver that water at lower cost," he said. He proposes more conservation in the south, supported with enough government money to make conservation work.

Los Angeles residents reduced water use sharply, and largely voluntarily, in the late 1970s during a major drought. Growers who have turned desert areas such as the Imperial Valley into breadbaskets by using water from the north could avoid the need for the canal by investing in new, more efficient irrigation methods, Willey said.

"Drip irrigation," for example, uses pipes to bring water directly to the roots of trees in an orchard, rather than wastefully flooding the orchard and letting the roots catch whatever soaks in near them.

But these sophisticated arguments continually succumb to the political passions of southerners, who see the north denying them water the north really does not need, and northerners, who fear the day when the south will demand more water than they have.

Mervin Field's California poll, taken in April, showed 40 percent favoring the canal, 34 percent opposed and 26 percent undecided statewide, but the differances between north and south were startling. In the north, 63 percent opposed the canal, with only 21 percent in favor. In the south, 53 percent favored the canal, with only 15 percent opposed.

The south's greater population gives it a natural advantage in such contests, and southerners often are contemptuous of northern sensitivities about water. One Los Angeles television commentator complained on the air about voters in Marin County, north of San Francisco, who had voted down bond isues for their own water supply.

"Now they have no water, their lawns are dying, they don't bathe regularly. They sit around smelling up their homes and griping about us. But the fact is, the water we use has nothing to do with their problem," the commentator said.

Both sides are organizing for a referendum, expected in November, on whether the canal will be built. Northerners are looking for southern environmentalists to help fight the canal, and southerners are looking for support from northern communities that use aqueduct water.

But the real battle, according to Thomas Graff of the Enviromental Defense Fund, may come after the canal had been approved and courts are forced to decide such isues as whether the state needs federal permission to build the canal and whether the canal will seriously affect wildlife in the deltas east of San Francisco Bay.