PITTSBURGH — Alcoa Inc. is being targeted by two foreign mining giants who are each preparing $40 billion takeover bids for the aluminum producer, a British newspaper reported. Alcoa shares rose nearly 6 percent Tuesday although some analysts questioned whether such a deal was likely.

BHP Billiton Ltd., the world's largest mining company, and Rio Tinto PLC, the world's second largest iron ore producer, both based in Melbourne, Australia, are said to be considering offers, the Times of London reported in Tuesday's editions, citing unnamed sources.

Alcoa shares rose $2.10, or 6.38 percent, to close at $35 Tuesday on the New York Stock Exchange after rising as high as $36.05 earlier in the session.

Officials with the mining companies declined to comment on the report Tuesday, as did Alcoa spokesman Kevin Lowery.

"We don't comment on rumors and market speculation," Lowery said. "It's not prudent to do so, nor is it productive."

Wall Street analysts Charles Bradford of Soleil-Bradford Research and Peter Ward of Lehman Bros. doubted such a takeover because BHP or Rio Tinto are focused more on the mining and raw materials end of the business than "downstream" industries like the manufacture of aerospace equipment and auto parts, which Alcoa emphasizes.

Ward also questioned the value of such a takeover because Alcoa shares have already increased 20 percent year to date, against a market that has grown just 1.4 percent.

"In our opinion, the risk/reward of these shares has now declined from attractive to average," Ward's note said.

Earlier this week, India's Hindalco Inc. agreed to buy Canadian aluminum producer Novelis Inc. for $3.6 billion in a deal that Hindalco said will make it the world's largest rolled-aluminum products manufacturer.

Bradford said the Hindalco deal might be fueling speculation that Alcoa could be the next aluminum products supplier to be gobbled up.

Bradford has revised his Alcoa earnings forecast up 15 cents to $3.20 a share for 2007, but said that was unrelated to the takeover speculation. Bradford on Tuesday downgraded Alcoa stock to "hold" based on what he called the "possibly erroneous" report in the Times.

The Times said takeover speculation was fueled by Alcoa's struggle to expand its business and a pending deal that would make Russia's OAO Rusal the world's largest aluminum producer, with about 12 percent of the global output of aluminum.