It is harvest time in the desert.

Now it is the sweet fruit of cantaloupe that is being brought in by the migrant workers, but at other times it is citrus, lettuce, wheat, alfalfa, sorghum. Today, rows of cotton are broken by the glint of sunlight reflected off standing irrigation water.

Blessed with rich soil and abundant water for irrigation, the people around Wellton produce, on average, a handsome $1,000 worth of crops a year on each of $65,000 acres of farmland reclaimed from the surrounding desert.

But it is costing American taxpayers increasing sums to maintain that food and fiber production, to the benefit of the 1,000 or so landowners here - the actual number of farmers if far fewer than that, because of absentee owners, such as trusts, churches banks, retirement funds and others who lease out their land.

A growing number of critics say that a $1 billion federal water project planned for the area could be avoided if those who do farm the land would change their agricultural ways.

The project is a 96-million-gallon-a-day desalting plant designed five years ago to reduce the salt content of the Colorado River. The river had become so salty it was endangering irrigated crops downstream in Mexico, and after protests from the Mexican government the United States agreed to act.

Now Congress is moving to increase funding of the plant to offset millions of dollars in cost overruns caused by inflation, design changes and errors. At the same time, there is growing sentiment that the plant could be substantially reduced in size and cost - or even eliminated - if farmers here would use irrigation water more prudently or perhaps grow different crops.

"We are convinced," says Jan van Schilfgaarde, director of the Agriculture Department's salinity laboratory, "that the time has come to realize we can't continue to use hugh capital and energy-intensive solution where [irrigation] management and social solutions will works."

The General Accounting Office reproted last month that Congress should "temporarily defer funding for this plant until the Bureau of Reclamation reevaluates if feasibility as well as alternatives which might provide a more economical solution."

Yet the Senate recently voted to increase funds for the plant by $83 million, more than the facility was expected to cost in the first place ( $62 million). Inflation has added $33 million more, and, combined with other efforts to meet the commitment to Mexcio, including a smaller test project now in operation east of Yuma, the government now plans to spend $333 4 million, compared to a $155.5 million estimate in 1974.

The Senate vote - one is expected soon in the House - reflected a basic decision by the Nixon administration and continued under President Carter: in the West, it is better to spend money than water.

In the West, hard-won and jealously guarded water rights and federal water projects are the wellspring of much of the region's growth, development and, therefore, money. And sentiment for the plant runs strong here, where water policies and farming practices are highly and politically sensitive.

So five years ago, federal officials rejected plans for the West to use less water - relatively small amounts - and therefore create fewer problems with Mexico. Instead, it was decided that all taxpayers would share the burden.

Says C. L. Gould, manager of the Wellton-Mohawk irrigation district, "Divided among the taxpayers, it's only $2.50 to $3.50 - even at $5 or $6 a family there just isn't the justification for making this amount of fuss.

"The federal government took on an obligation [to Mexico] which was not theirs to take."

In 1948 the United States agreed in a treaty to assure Mexico that when the Colorado River crosses into the Mexicali Valley, there will be enough flow left to irrigate 1.5 million acres with water one foot deep. For 17 years, more than enough river water flowed to Mexico annually, but in 1961, when the United States began filling Lake Powell on the Utah-Arizona border, less water moved downstream.

At the same time, Wellton-Mohawk began discharging salty, used irrigation water into the Colorado. The Mexican government protested.

In 1974, the United States agreed to reduce the salt content, and the desalting plant was decided on.

Van Schiligaarde opposed it then, and he opposses it even more now. Crop yields, he said in an interview in his Riverside, Calif., office, can be maintained on less water. For example, citrus trees once given 10 feet of water a year need only six feet at the most, he said.

Farming technology and techniques are available now, he said, "that could essentially solve the problem - have the same effect on the river as the plant."

His views have been taken up by Rep. George Brown (D-Calif.), who has waged a battle, a lonely one so far, and acknowledges he does "not relish getting into this issue because it is complicated, time-consuming and politically messy."

Brown estimates that operating costs over the next 50 years will make the desalinization plant, to be built just west of Yuma, a $1 billion project benefiting roughly 150 farmers. (Gould of the irrigation district questions that estimate.)

Brown also says the plant will consume large amounts of electricity at a time of an energy shortage. Now more than four years behind schedule, the plant has been pushed forward without any idea until recently of where that electricity will come from.

The legislation increasing the funding for the plant provides for it to get power from a federal coal-burning facility on a nearby Navajo Indian reservation. Congressional budget watchers say this means the United Stattes will lose $1.8 million in revenue a year because the power could have been sold to others.

Van Schilfgaarde's suggestions include the use of more modern irrigation equipment and sophisticated field plowing - for example, using laser beams to make a field absolutely level, thus reducing its need for water. Some fields in the Wellton-Mohawk district have been plowed using lasers, and as a result the same amount of irrigation water does three thimes the work as before.

Alternatives offered by others include:

Buying the 65,000 acres and telling farmers what to grow and how much water they can use. Ten thousand acres already have been bought by the government and taken out of production to reduce salty discharges.

Buying the water rights from farmers and then telling them how they can use the water.

Those prospects do not rest well in a region that professes its independent and ruggedly individualistic spirit.

"People have been here for three generation," says Gould. "They came out to develop the West. They put their blood, sweat and tears into it."

Gould portrays his irrigation agency and the 5,000 inhabitants of the desert valley more as victims in the current dispute than as the source of a problem." All of these people," he says of farmers along the 1,400 miles of the Colorado River, "are contributing to the salt problem, but we're the ones at the bottom of the pool.

"People say, 'Look at all this money being spent for a handful of people' and say it's our obligation. It is not our obligation. The federal government assumed the obligation to accommodate its relations with Mexico."

Gould scoffs at van Schilfgaarde's irrigation management ideas as unproved; van Schilfgaarde disagrees. Critics say the salt plant itself is a risk, because no desalting plant this big has ever been built.

Even officials of the Interior Department's Bureau of Reclamation, which is responsible for the plant's construction, acknowledge that the desalting facility is not the only possible soultion.

They say, though, that political problems make it the only practical one. "What may be economically attractive," says Roy D. Gear of the bureau's Boulder City, Nev., office, which is in charge of the project, "isn't always politically viable."

Thus notions such as buying up land or having the seven states supplied by the Colorado River give up their legal allocations of water are politically doomed. No one suggests reneging on the agreement with Mexico, particularly as that nation continues to develop oil and gas.

With the Colorado running strong now, the water is within the limits agreed to by the two nations.

But it won't last, as the 242,000 square-mile Colorado River basin continues to grow. Taking water from the river and returning to it salts leeched from the ground. Thus the long-range question is whether the solution to the salt problem is more expensive construction projects or better use and management of the water up and down the river.

The current battle over the Yuma desalting plant may not represent the end of a war, only the beginning. CAPTION: Picture 1, Small plant east of Yuma tests desalting process to be used in larger project. Billy Curry - The Washington Post; Map, no caption, The Washington Post; Picture 2, Irrigation water is the difference between desert and a field of ripe cantaloupe. Picture 3, Laser - leveled fields make more efficient use of precious irrigation water.