BILLINGS, Mont. - Two North Dakota energy companies reportedly are making an offer to buy NorthWestern Corp.'s utility properties in Montana and possibly in South Dakota as well.

MDU Resources Chief Executive Martin White, Basin Electric Cooperative Chief Executive Ron Harper and several Montana co-op executives will hold a news conference Monday at the Hampton Inn in Helena to announce the offer, the Billings Gazette reported Saturday.

The newspaper did not identify its sources.

Neither White nor Harper could be reached for comment.

MDU spokeswoman Linda Donlin would not comment on the report but said MDU is always looking at companies to buy.

NorthWestern spokesman Roger Schrum said NorthWestern has received no proposal and had no comment on the report.

NorthWestern executives have said repeatedly the company is not for sale, even after they filed for reorganization under federal bankruptcy laws in Delaware on Sept. 14.

NorthWestern bought Montana Power Co.'s distribution system for $1.1 billion almost two years ago and now serves about 300,000 electric customers and 157,000 natural gas customers in Montana. The company owns no generating plants in the state.

Basin Electric, serves 1.4 million customers in nine states, also owns no power plants in Montana.

MDU operates several subsidiaries. A major operation is its electric and natural gas utilities, Montana-Dakota Utilities Co. and Great Plains Natural Gas Co., which serve the Dakotas, Montana, Minnesota and Wyoming.

Montana co-ops tried to buy the last energy assets of the former Montana Power, but lost out to NorthWestern Energy.

"Electric cooperatives in Montana have already expressed an interest in buying certain NorthWestern territories in this state," said Dave Wheelihan, executive director of the Montana Electric Cooperatives Association in Great Falls.

About 15 of Montana's 26 rural electric co-ops are members of Basin Electric, which sells wholesale power to several Montana cooperatives from its power plants in North Dakota and Wyoming, he said.

"There has been speculation about a number of different utilities being interested in the (NorthWestern) system, so it doesn't surprise me to hear MDU is making an offer," said Tom Schneider, vice chairman of the Montana Public Service Commission.