HELENA - A new Montana law banning the federal government from buying state land is unlikely to change how much land U.S. agencies own in Montana, federal and state officials say.

The measure, part of a bill Gov. Judy Martz signed, is intended to prevent federal agencies from purchasing any state land put up for sale, but land managers say such sales to the federal government haven't occurred for decades in Montana, and federal agencies have shown little interest in acquiring more land in the state.

Bud Clinch, director of the state Department of Natural Resources and Conservation, said land ''swaps'' with the federal government are more common, and nothing in the new law forbids those from continuing.

Clinch also said the ban doesn't prevent a private landowner or organization from buying state holdings and then selling them to the federal government.

The prohibition was an amendment Rep. Rick Maedje, R-Fortine, successfully added to a bill creating a new ''land banking'' program. That measure allows the state to sell up to 100,000 acres over five years and use the proceeds to buy more attractive parcels. The state can stockpile money from the sale of no more than 20,000 acres before buying new land.

Maedje, a logging contractor, said he believes Montana is the first state to outlaw sales of its land to the federal government. And it's about time, he said.

''The concern from northwestern Montana is that we have nothing but trouble with federal land ownership in our area,'' Maedje said.

Clinch, however, dismissed the new ban as inconsequential.

''Nobody from the federal government has expressed interest in buying state land,'' Clinch said. ''I don't think federal agencies are looking to aggressively expand their ownership.''

The two agencies owning almost all of the nearly 26 million acres of federal land in Montana agreed with Clinch's assessment.

Paula Nelson, spokeswoman for the regional office of the U.S. Forest Service in Missoula, said the new state ban poses no problem for her agency.

''We do land exchanges rather than purchases,'' she said.

Greg Albright, spokesman for the Bureau of Land Management in Billings, said the same is true for that office.

''It would be rare for BLM to ever be a customer to purchase,'' he said. ''When we try to acquire land, it's usually through an exchange.''

Clinch said the state has done only two land trades with the federal government over the past 10 years, and he knows of no sales for decades.

But Maedje said he hopes his ban will nudge the federal government toward better management policies and prevent its agencies from laying claim to more land. The more tax-exempt federal land Montana has, the greater the burden on other taxpayers, he said.

''The state has a right to protect the property tax base within its borders,'' Maedje said. He added that he would like to see the next Legislature pass a law requiring continued taxation of any private land bought by federal agencies.

Rep. Chris Harris, D-Livingston, was a leading critic of Maedje's amendment, saying it was more symbolic than practical.

''This is a thumb-our-nose at the federal government,'' he said. ''We don't like the federal government and this is one way of showing our disrespect.''

Clinch said he recognizes the distaste some people have for the federal government in a state where federal ownership accounts for about 28 percent of the 93 million acres of land.

''Some people are very bothered by that, and that can create an incredible public backlash that far outweighs any benefit from those limited number of sales'' that might occur, he said.

Maedje insists he neither mistrusts nor dislikes the federal government, only its land management practices.

Dan Kemmis, director of the Center for the Rocky Mountain West, said Maedje's views are not uncommon in Montana and other Western states.

''The federal government owns far more of the West than any other region, and the interior West was settled by people with a strong strain of individualism,'' he said. ''You have a recipe for major tension.''