Bolstered by a study that shows that western cattlemen are paying far less than market value for grazing their herds on federal lands, the Interior Department is preparing to recommend changes in the 80-year-old program.

The effort has the support of conservation groups, who have long complained that low fees encourage overgrazing of fragile range lands. It also has the blessing of the Office of Management and Budget, which sees the grazing program as a red-ink proposition.

"In all fairness to the taxpayer, these grazing fees are too low," OMB spokesman Edwin L. Dale said. "It has been our position for . . . years that these fees, as well as other user fees, have been far below their . . . value."

But the idea has its detractors, most notably the National Cattlemen's Association, which has managed to fend off repeated efforts to increase the grazing fee.

According to the study, prepared by the Bureau of Land Management (BLM) and the U.S. Forest Service, grazing an animal on Uncle Sam's pasture can cost one-fifth what it would cost on privately rented land.

Last year, grazing fees brought in $26 million from 310 million acres of range land, less than half the $56 million it cost the BLM and the Forest Service to operate the program.

The grazing fee is $1.35 a month per "animal unit," which means one cow or cow-calf pair, one horse or five sheep. The rate is so favorable, according to some conservationists, that ranchers holding grazing permits can sublease them for a healthy profit -- as high as $8 a month per animal unit.

Moreover, according to Sierra Club represenative Rose Strickland, ranchers who take good care of their range lands "are treated the same as those who abuse them."

The cattlemen aren't ruling out a modest increase in the fees. But in their quest to to preserve the method of calculating fees, they have some high-ranking champions.

Sen. Paul Laxalt (R-Nev.), a longtime friend of President Reagan, said the current formula "has served us well and we should retain it."

The cattlemen are especially wary of proposals that the government rent out its pasture under a competitive bid system. Two federal grazing areas currently are leased competitively -- one at Fort Meade, S.D., and the McGregor range in New Mexico -- and both bring in substantially more in grazing fees than other federal range lands.

Bids for the Fort Meade land were nine times the amount that would have been collected from the standard $1.35 per animal unit; in the McGregor range, revenues approached five times the standard amount.

Competitive bidding isn't the only possibility for handling grazing fees, however. The BLM-Forest Service report -- the seventh major study on the issue since 1920 -- lists six potential methods of calculating grazing fees.

The potential revenues differ according to how the calculations are done. In the recent appraisal report, the values ranged from $5.20 a head per month to $9.50 a head per month.

The lowest rate would have increased revenues in fiscal 1985 from $26 million to $99 million. If the $9.50 figure had been used, the fiscal 1985 revenues would have increased to $200 million. For its fiscal 1986 budget, the OMB projected that grazing fees would increase to $63 million.

Though a number of House members and senators from western states were contacted for their opinion on the issues of competitive bidding, subleasing of grazing permits and leases owned by certain ranchers, most declined to comment and several stated that they weren't interested in the issue.

The number of cattlemen involved might have some bearing on that lack of response. Stockmen using public range land make up 2 percent of the nation's livestock producers. In the 16 western states, they represent less than 5 percent of the livestock producers.