Bethlehem Steel, the second largest US steelmaker, on Monday agreed to pay $400 million in cash and stock for rival Lukens, marking the biggest acquisition in the countrys steel industry in recent years. Lukens, a specialist maker of steel plate and stainless steel products, has been hit by the surge in stainless steel imports, which has depressed prices in the US. Bethlehem said it would sell Lukens stainless steel operations after the acquisition. The agreement, which will also include the assumption of $250 million of Lukens debt, reflects the pressure on traditional integrated steel makers such as Bethlehem to cut costs and close inefficient plants in the face of mounting competition from both foreign producers and new mini-mill companies in the US.