KERSEY, Colo. (AP) _ Two billionaire families more closely identified with the boardroom than the barnyard are facing off over construction of one of the most technologically advanced hog farms in the United States.

The Bass brothers of Fort Worth, Texas, are building a hog and cattle farm along the banks of the South Platte River in northeastern Colorado's Weld County that plans to raise 300,000 pigs and 10,000 cattle a year.

''This is something very unique,'' says Jack Schneider, effluent manager for the hog farm. ''It has its own ecosystem, utilizing as much nitrogen as possible to go back into grass production, so we can raise cattle.''

But downstream are the 32,000-acre Eagle's Nest Ranch with 700 head of cattle owned by billionaire Philip Anschutz, owner of Southern Pacific Transportation Co., and the 760-acre Windbreak Ranch owned by beer magnate Peter H. Coors of Adolph Coors Co.

They claim that National Hog Farms, which is building the new farm, is trying experimental farm techniques and if the experiment fails, it could pollute their land.

The farm plans to use no antibiotics or other drugs on the animals, which are commonly used elsewhere. It also plans to spray waste water on the land to fertilize native grasses, which in turn would feed cattle.

Coors and Anschutz are financially backing environmentalists who oppose the operation, and have filed lawsuits in a yet-unsuccessful attempt to block it.

Weld County Commissioner Gene Brantner calls it a duel between billionaires that the county wants no part of.

''Let them go down to the courts to decide who is right or wrong,'' said Brantner, whose family helped settle the county and is featured in James Michener's novel ''Centennial.''

The issues involved - land and water - are as old as Colorado, and important in a region that receives only 15 inches of precipitation annually.

Also at stake are 200 jobs provided by the new hog farm, a crucial factor in an economy that has been hit hard the past few years by declines in the oil industry and land values.

The farm, scheduled for completion in 1992, would have its own weather station and sewage treatment plant. Trucks entering the farm will be disinfected and workers will be required to shower and change into sterile clothes before entering. Grown hogs will be transported to neighboring states for slaughter.

''They're on the leading edge, doing things that haven't been done in other places,'' said Schneider. ''I can't say 100 percent sure something won't go wrong, but if it does, it will be minimal.''

Financial backers include investor Robert Bass, whose wealth has been estimated by Forbes magazine at $1.44 billion; Sid Richardson Bass and Lee Marshall Bass, who are valued at an estimated $1.25 billion; and Edward Perry Bass, at $1 billion. They made their money in oil, gas and farming.

Anschutz has a net worth of $1.2 billion and Coors owns or controls properties worth further millions. Both have refused to comment publicly on the battle, preferring to work through environmental groups and the courts.

They're worried about the 2.2 million gallons of waste water the farm will generate each day and the 24-hour holding capacity in the sewage tanks. The concern is that if those tanks fail or break down, the wastes could wind up in the wells from which the Anschutz and Coors ranches pump their drinking water.

They're also afraid the hog farm will harm the pheasants and geese they like to hunt on their property, the fish they catch in their private ponds, and the nearby Riverside reservoir, a refuge for geese and pelicans.

They point to the National Hog Farms operation in Atkinson, Neb., which has been sued five times for air pollution, water pollution and allegedly causing pseudo-rabies, resulting in a quarantine of that farm's hogs.

Coors and Anschutz are financially backing an organization called Protect Our Water, which has started a petition drive to regulate what they say was an unforeseen development in American farming.

Schneider admits some of the farming techniques are experimental, but says the theories are sound.

The farm has built 16 monitoring wells to check for ground water contamination. The weather station will have solar panels to monitor irrigation to match water usage. The hog units will be air conditioned and hermetically sealed to keep out disease, while refrigerated trucks will dispose of dead animals.

Robert Stovell, who manages the Eagle Nest Ranch for Anschutz, said National Hog Farms also tried experimental techniques in Nebraska and some of those failed.

Schneider acknowledged there have been problems in Nebraska, most stemming from the use of lagoon drainage for wastes. He said the company learned a lot from those mistakes and corrected the problems in the new operation.

Stovell acknowledged that the South Platte River, a main focus of the current battle, already is polluted, partly from cattle operations farther upstream.

''We're not totally opposed to the company in this case. If they set up adequate handling facilities, that's fine,'' Stovell said.

Stovell said he will continue his petition drive and lawsuits against the operation, although he hasn't had much luck because the facility meets county regulations.

Stovell said stricter regulations don't exist because no one foresaw scientific corporate farms like this. He wants county regulations changed to control the amount of wastes that can be released.