BILLINGS — The director of Montana’s land agency said Tuesday that a quarter-mile buffer will be required of companies drilling on 16 oil and gas leases for sale along the Yellowstone River and other central Montana waterways.

Two conservation groups, Montana Trout Unlimited and the Greater Yellowstone Coalition, had asked the state to defer its Sept. 9 sale of the 16 leases along with eight more. They said drilling could damage nearby trout fisheries.

The groups’ protest against the sales is part of a campaign by environmental and sporting groups to slow oil and gas leasing on public lands in the West.

That effort — at times pursued in Montana in concert with the state Department of Fish, Wildlife and Parks — has yielded mixed results. Some sales have been delayed or held with restrictions attached to leases, while others have proceeded unaltered.

Mary Sexton, director of the Department of Natural Resources and Conservation, said the buffers included in the September sale would allow drilling while answering the concerns over trout populations.

However, Sexton added that the state owns only patches of land in the area. She said the restrictions would have little practical effect unless private landowners and the Bureau of Land Management adopt similar measures.

Trout Unlimited’s Michael Gibson said Tuesday that the quarter-mile buffers offered “a step in the right direction,” but did not include enough waterways. Left out were a number of smaller streams that Gibson said have viable populations of Yellowstone cutthroat trout.

“We’re moving into a pretty sensitive area for oil and gas development, and we would like to see some of the leases deferred for six months until we can sit down and come up with a plan to protect these areas,” Gibson said.

Drilling rights on the parcels are being sold in part to generate revenue for Montana’s school trust program, which brings in $25 million to $35 million annually through mineral lease sales.

The buffers would prevent any oil and gas wells, roads or other infrastructure within a quarter mile of waterways. Sexton said she would require buffers only along the Yellowstone, Shields and Boulder rivers and their direct tributaries.

“They’re looking at every stream, whether it’s intermittent or perennial or whatever it might be,” she said. “We’re looking at the navigable waterways and their direct tributaries.”

Previously, the state has sold approximately 6,000 acres of riverbottom leases along the Yellowstone. Sexton said at least 14 wells have been drilled on those leases.

No wells are producing significant quantities of gas on the Boulder or Shields rivers, said Tom Richmond with the Montana Oil and Gas Conservation Board.

However, the Bill Barrett Corp. of Denver has drilled three exploratory natural gas wells along the Shields River and has plans for at least one more, according to company filings with the federal Securities and Exchange Commission.