MORGANTOWN, W.Va. — Wheeling-Pittsburgh Corp. announced Thursday it has a tentative agreement to merge with Brazilian steelmaker Companhia Siderurgica Nacional, just weeks after a Chicago-based steel supplier launched a hostile takeover attempt.

Wheeling-Pitt argues a deal with CSN would create a more flexible cost structure, a guaranteed stream of slab steel and much-needed cash for capital improvements. But any merger must be approved by shareholders, federal regulators and the United Steelworkers.

Wheeling-Pitt shares shot up more than 8 percent in morning trading on the Nasdaq Stock Exchange, from $21.28 to $23, while CSN shares fell just a fraction of 1 percent to $32.12 on the New York Stock Exchange.

Under terms of the proposed merger, CSN would take 49.5 percent ownership of the new company, while Wheeling-Pitt shareholders will control the other 50.5 percent.

About $150 million of CSN's $225 million cash investment would be used to upgrade and expand Wheeling-Pitt's hot strip mill capacity to 4 million tons, and to add a second galvanizing line at CSN's processing plant in Terre Haute, Ind., Wheeling-Pitt CEO James G. Bradley said.

That should ensure steelworkers that Wheeling-Pitt "is not only planning to be successful tomorrow, or next year, but has a vision to build a company that will be successful for the next generation of Wheeling-Pittsburgh steelworkers," he said.

But Ken Aspenlieter, president of USW Local 1190 in Steubenville, Ohio, said it's too soon for the union to form an opinion on either partner. That may take months.

Though the USW has had a direct meeting with the other suitor, Esmark Inc., none of the presidents of the five union locals has had a meeting with CSN, Aspenlieter said.

"This will be the first time we saw any details from CSN, to be honest with you," he said. "We always knew CSN was in the picture ... but as far as how far in, we had no knowledge."

The lack of a direct role concerns the union, he said.

"We're involved in this also," Aspenlieter said. "We would like to talk to them. It's always better when you see somebody face to face."

Wheeling-Pitt says the deal would add 900,000 tons of capacity for cold-rolled steel to its 3.4 million tons of capacity for hot-rolled steel. Wheeling-Pitt also produces about 2.8 million short tons of slab.