Federated Department Stores Inc.'s board, rebuffing a takeover bid by Canadian real-estate developer Robert Campeau, yesterday approved a merger with R.H. Macy & Co. in a deal worth about $6 billion.

But Campeau, who has been pursuing Cincinnati-based Federated for a month, immediately increased his offer to Federated's shareholders.

Wall Street analysts yesterday said it was still uncertain who would win the company, which contains some of the most prized stores in America, including Bloomingdale's, I. Magnin and Abraham & Straus.

"I don't think the Macy's-Federated deal is a done deal," said Edward A. Weller, an analyst at Montgomery Securities.

Both Macy's and Campeau's bids are worth about $6.1 billion, but comparing them is difficult because of their complicated structures.

Macy's has offered to pay $74.50 per share for 80 percent of Federated's stock, with the remaining shares to be exchanged for stock in a newly created company that would be called Macy's/Federated. The value of that stock has not been determined.

Campeau said late yesterday he would pay $75 a share in cash for 80 percent of the stock, then buy the remaining shares for $44 apiece.

"Macy's bid is not competitive and we intend to prevail in the marketplace," a Campeau spokeswoman said yesterday.

Neither Macy's nor Federated would comment on Campeau's increased bid.

Federated stock closed yesterday at $66.75, down $1, in heavy trading on the New York Stock Exchange.

Analysts said Campeau, who showed his persistence in his successful attempt to buy Allied Stores Corp. in 1986, was likely to keep fighting for Federated.

"Campeau is not the kind of guy who goes away," Weller said. "He is very persistent in the pursuit of his prey."

Campeau "wants Federated badly," said Monroe Greenstein, an analyst at Bear Stearns & Co. "He's already given up a lot to get it."

To assemble financing for his takeover offer, Campeau has sold a partial voting interest in his Campeau Corp. to Toronto's wealthy Reichman family and has agreed to sell one of Allied's most profitable chains, Brooks Brothers, to Britain's Marks & Spencer PLC for $770 million if he wins Federated.

Nonetheless, some retail analysts were betting Macy's would win.

"If pressed to the wall, I'd bet on Macy's," said Tom Tashjian, of Seidler Amdec Securities Inc. "Federated's management recognizes it's in the company's and customers' best interest to put Federated in the hands of another retailer instead of in a real estate-driven company," which would probably sell more of Federated's assets to finance the deal than Macy's would.

Under the agreement reached yesterday with Macy's, Federated has a strong financial stake in making sure Macy's wins: Federated agreed to pay up to $45 million in Macy's expenses if the merger falls through for any reason other than a Macy's default or failure to obtain financing.

However, Campeau said he intended to bring a lawsuit against this provision. If the fee is invalidated or withdrawn, Campeau said he would increase his bid by about $2.20 a share for the remaining 20 percent of the shares not initially submitted to him.

Federated executives also would be given severance packages known as "golden parachutes" by Macy's if the deal goes through. Chairman Howard Goldfeder, for instance, said at a news conference in Cincinnati yesterday that he would be paid $3.1 million when he steps aside after a Macy's-Federated merger is completed.

Federated's decision to merge with Macy's, which emerged as a surprise bidder Monday, was made after a daylong board meeting Tuesday. "In approving the transaction, the Federated board of directors was particularly impressed with the potential long-term benefits which would be made available to Federated stockholders through this combination," Goldfeder said in a statement.

Even so, financial analysts predicted yesterday that no matter who won the highly coveted company, it was a certainty that many of its divisions would have to be sold off to help finance the deal.

The first candidates would probably be Federated's nondepartment store operations, including Ralph's supermarket chain and Gold Circle, a discount-store chain.

In either case, department-store operations would probably be sold, although some analysts predicted Campeau would sell more of Federated's operation if his bid is successful than Macy's would.