TORONTO, FEB. 26 -- Campeau Corp. today agreed to boost its takeover bid for Federated Department Stores Inc. to $6.1 billion and appeared close to sealing a friendly deal to acquire America's fifth-largest retailer.

Campeau, moving to end a costly and bitter monthlong quest, said it agreed to pay $68 a share and was negotiating other terms with the Cincinnati-based parent of upscale chains such as Bloomingdale's and I. Magnin.

Cautioning that the talks could break down, a spokeswoman for Campeau said the Toronto-based developer was negotiating toward an agreement that could go to the Federated board Monday. Federated spokesmen confirmed the negotiations.

"The price has been agreed upon but because negotiations are going on, everything could fall apart," said the Campeau spokeswoman. "But they're close to completing."

Monroe Greenstein, a retailing analyst at Bear, Stearns & Co., speculated that Federated buckled to Campeau after considering a corporate recapitalization and deciding it would not work. "There probably was no other firm offer on the table," he said.

The proposed acquisition would be the sixth-largest corporate takeover ever, behind U.S. Steel Corp.'s $6.6 billion acquisition of Marathon Oil Co. in 1981.

Campeau Chairman Robert Campeau has said he would merge Federated and Allied Stores Corp. of New York, which he acquired in 1986 for $3.5 billion. Such a concern would initially have combined annual sales of about $14.7 billion and would include such well-known retail names as Bloomingdale's, Ann Taylor and other chains.

An agreement between Campeau and Federated would end a complex battle that began Jan. 25 when the Canadian bid $47 a share, or $4.2 billion, in a tender offer. Last week he raised the bid to $61 a share, or $5.5 billion, and then to $66 a share, or $5.9 billion.

Analysts doubted negotiations would fall apart at this point.

"Sixty-eight dollars all cash is a very nice price," Greenstein said. Federated shares traded at $35.87 1/2 on the last trading day before Campeau's initial bid.

Federated stock yesterday rose $1.375 to close at $64.50 on the New York Stock Exchange. Campeau common stock jumped the equivalent of 78 cents to close at $17.36 on the Toronto Stock Exchange.

Greenstein speculated that Campeau, who cut 16 Allied divisions -- including Washington's Garfinckel's department store -- within about a year of that acquisition to pay off heavy debt, would retain Federated's most valuable assets but "there will be a major restructuring of the organization."

If Campeau wins Federated, he will lose Allied's prized Brooks Brothers chain. Campeau agreed earlier this week to sell the operation for $770 million to Britain's Marks and Spencer PLC to help finance the Federated deal.

"He'll have gained Bloomingdale's, which is a lot bigger and more important than Brooks Brothers," Greenstein said.