TORONTO - Alcoa Inc., seeking to keep pace with growing Russian rival Rusal, launched a hostile $27 billion bid yesterday for the Canadian aluminum company Alcan Inc., after failing to negotiate a deal during almost two years of private talks.

Alcan's U.S. shares rose 35 percent, well above the offered price, suggesting investors believed the bidding could go higher. Alcoa shares gained 8 percent.

Alcan, of Montreal, said its board "will consider the proposal" and advised shareholders to await its recommendation.

Alcoa, which has headquarters in New York but most of its corporate operations in Pittsburgh, said the proposed cash-and-stock deal would create a premier diversified global aluminum company that could grow faster than the two companies could on their own.

"I'm disappointed that we were not able to come to a negotiated transaction," Alcoa chief executive officer Alain Belda said, "and while I'm taking this offer to shareholders, I hope that this combination can move forward with the support of Alcan management and board."

The combined company, with 188,000 employees in 67 countries, would have had revenue last year of $54 billion and earnings before interest, taxes, depreciation and amortization of $9.5 billion.

The combined company's alumina capacity would be about 21.5 million metric tons, and its aluminum capacity would be about 7.8 million metric tons. Alumina is used to make aluminum. A metric ton is about 2,204.6 pounds.

Until recently, Alcoa and Alcan were the world's top two producers of aluminum, but they now lag behind Rusal, of Moscow. Rusal, its rival Sual and Swiss-based commodities trader Glencore International AG completed the combination of their assets at the end of March, creating United Company Rusal and surpassing Alcoa as the world's largest aluminum producer.

The Alcan deal would vault Alcoa past Rusal in aluminum production.

"The reality is that commodities businesses are consolidating globally," Morningstar Inc. analyst Scott Burns said. "When foreign countries like Russia allow their two largest aluminum producers to merge and really dominate that market, and you've got a company called Chalco in China where the Chinese government has made no secret that they want this to be a national champion, I think it really gives a company like Alcoa a nice leg to stand on in terms of regulatory objection."

Alcoa, which plans to maintain dual headquarters in Montreal and New York, said it saw annual pretax cost savings of about $1 billion from its proposed combination with Alcan in the third year after the deal closed.

Belda said the deal would "significantly deepen an already extensive commitment by both companies to Canada, and it will ensure Canada remains a world leader in the mining and metals industry."

Alcan has a big presence in the French-speaking province of Quebec, and approval could be difficult because of nationalist sentiment there.

The transaction is subject to review by antitrust authorities in the United States, Canada, the European Union, Australia and Brazil, as well as foreign investment clearance in Canada, France and Australia.

Alcan's U.S. shares rose $21.08 to close at $82.11 yesterday - above the offered price - while Alcoa shares gained $2.97, to $38.63.