Brazilian steelmaker Gerdau offered to pay up to $1.7 billion to take full ownership of its North American unit, looking to reduce borrowing costs and increase efficiency.

Gerdau on Wednesday bid $11 per share in cash for the 33.7 percent of Gerdau Ameristeel stock it does not already own. The offer represents a 53 percent premium to Ameristeel's closing share price on Tuesday.

Ameristeel shares surged 54.7 percent to $11.09 in New York, while Gerdau's most traded preferred shares were up 1.9 percent to 24.71 reais in Sao Paulo.

Rio de Janeiro-based Gerdau acquired its majority stake in Ameristeel in 1999.

By integrating its North American unit into the Brazil-based holding, Gerdau is seeking to streamline operations, reduce borrowing costs and gain in efficiency, analysts said. The company was hit hard by the global recession that crippled activity in the housing market in the United States, where Gerdau earns about a third of its annual revenue.

They are moving forward ... because they foresee a solid economic recovery in the United States that the market doesn't, said Marcos Assumpcao, an analyst with Itau Securities in Sao Paulo. He said a fair premium for the Ameristeel shares would be 20 percent to 30 percent.

This is obviously positive because North America has large idle capacity that needs to be put in operation, while the group needs to supply Brazil with more long steel, he said.

Gerdau plans to pay for the takeover with cash on hand and loan commitments already arranged with banks. As a wholly-owned unit, Ameristeel would benefit from Gerdau's higher corporate debt ratings, the Brazilian company said.

Gerdau's foreign debt is rated BBB-, the lowest investment grade rating, by Fitch Ratings and Standard & Poor's. Ameristeel is rated BB+ by S&P, the highest junk rating and one notch below Gerdau. Fitch does not rate Ameristeel.

(Reporting by Elzio Barreto and Guillermo Parra-Bernal)