It was plain old-fashioned horse-trading yesterday when House and Senate negotiators sat down to put finishing touches on the 1991 Interior appropriations bill, which passed both houses late last night.

The House conferees gave up their proposal to raise grazing fees for western cattlemen on public lands. In return, the Senate gave up its opposition to keeping millions of acres off limits to offshore oil and gas development.

Heartland senators, led by Harry Reid (D-Nev.), were united in stopping the House-proposed hike in grazing fees, which are now as low as $1.81 an animal a month on Forest Service and Bureau of Land Management property. But when the conferees broke up Friday night, it looked as if the heartlanders would have to accept a small increase to a fee of not less than $2.

Meanwhile, oil-and-gas-state senators, led by J. Bennett Johnston (D-La.) and Ted Stevens (R-Alaska), thought the House conferees had backed down on their insistence on the offshore oil and gas moratorium. But when they reconvened yesterday morning, the heartland senators had struck a deal with House and Senate conferees from coastal states, who supported the moratorium for environmental reasons.