NiSource Inc., a Midwestern energy company that owns Indiana's largest utility, said yesterday that it is extending its hostile takeover bid for natural gas company Columbia Energy Group until midnight Feb. 11.

The move was expected, since NiSource had signed a confidentiality agreement with Herndon-based Columbia Energy, essentially putting its offer on hold until March 1 to allow Columbia's board of directors to consider offers from NiSource and other potential bidders.

According to analysts, Dominion Resources Inc., which includes Virginia Power, also has signed a confidentiality agreement with Columbia, which has extensive gas storage and transmission facilities and which sells gas to about 2 million customers in Maryland, Virginia, Pennsylvania, Ohio and Kentucky.

Early this year, Dominion and Columbia Energy went head to head in a takeover fight for Consolidated Natural Gas Co. of Pittsburgh, which Columbia lost. Dominion's acquisition of CNG has received all the regulatory approvals it needs and is expected to close early next year, said Dominion spokesman Mark Lazenby.

Lazenby declined to comment on whether Dominion has signed a confidentiality agreement with Columbia, but Merrill Lynch & Co. analyst Steven L. Fleishman said Dominion managers had told analysts that they are looking at Columbia. Dominion management met with industry analysts earlier this month in New York.

"The strategic rationale for putting the systems together makes sense," Fleishman said. But Fleishman said he doubts Dominion will pursue a takeover of Columbia. "The financials and the way it is structured has to make sense, too," he said.

NiSource said it had received backing from the owners of about 61 percent of Columbia's shares for its $6.1 billion takeover bid. NiSource raised its bid for Columbia Energy from $68 to $74 a share in October, but Columbia rejected both offers as inadequate.

Since then Columbia Energy has thrown open the door to other potential bidders to talk about "possible strategic transactions, including mergers and other business combination transactions and purchases of a material amount of the company's stock or assets."

"Everybody's in there looking now," said Edward J. Tirello, an industry analyst with Deutsche Banc Alex. Brown Inc. in New York.