LISBON/SAO PAULO - Brazil's CSN (CSNA3.SA) (SID.N) offered on Friday to buy Portuguese cement producer Cimpor (CPR.LS) for 3.86 billion euros ($5.6 billion) as the steelmaker slowly diversifies from its core business outside its home base.

The bid underscores efforts by CSN's Chief Executive Benjamin Steinbruch to grow in areas other than steel and mining. It also marks the company's biggest effort to date to expand overseas after the failed takeover of Corus Plc in 2007, taking advantage of depressed valuations of construction assets worldwide.

If the acquisition goes as planned, Cia. Siderurgica Nacional, known as CSN, could turn itself into a global cement market player, analysts said. The former state company, sold to private investors in the 1990s, is Brazil's second largest maker of flat steel and has a sizable iron ore operation.

This is a purchase for the long term. That's the way they see it, said Pedro Galdi, who covers steel, mining and construction for Sao Paulo-based brokerage SLW Corretora. Europe is doing badly now, but it probably won't within the next five or so years.

Under terms of the unsolicited cash bid, Sao Paulo-based CSN offered to pay holders of Cimpor's 672 million shares 5.75 euros each, representing a premium of 5 percent over Thursday's closing price. The offer is about 10 percent bigger than the average share price of Cimpor's stock over the past 30 days.

Cimpor shares soared 16 percent to 6.34 euros, suggesting CSN will have to sweeten its offer to win the company. CSN's stock posted its biggest decline since January 12, shedding as much as 6.6 percent to 55.17 reais.

CSN's Managing Director Juarez Avelar told Reuters the company expects little difficulty in buying the stake. The company considers the price for Cimpor fair and would not enter into a bidding war for the stake, he said.

We are very confident. We think that getting to 50 percent will not be complicated, Avelar said.

Brazilian companies are increasingly growing their international business as Brazil's real gains ground against the dollar, and the government stimulates creation of conglomerates able to compete globally in paper and pulp, steel, iron ore and food processing.

Cimpor, which has net debt of 1.8 billion euros, is Portugal's biggest cement maker and operates in Brazil, China, Egypt, South Africa, Spain, and Turkey. Some of those countries are undergoing their worst housing downturns in decades.

Analysts said Steinbruch's appetite for risky acquisitions as well as his record of long shareholder disputes with partners may make investors wary about the Cimpor plan.

CSN said after the bid was unveiled that it would fund the Cimpor takeover through cash in hand and bank loans.

Assuming Cimpor's debt, CSN might have to pay a total $8.1 billion, which JPMorgan Chase analysts said may be a step that is just too large to be taken now.

The price might be too high for the goal and the goal isn't too clear for us, said Antonio Emilio Ruiz, a steel analyst for Banco do Brasil's securities unit.

CSN canceled a conference call with analysts that had been scheduled for earlier on Friday to explain the rationale for the acquisition.

The bid hinges on winning 50 percent plus one share in Cimpor, the company said.

BRAZIL SPREADING ITS WINGS

Companies in Brazil are expanding as government plans to build roads, ports, railway and hydropower projects are bringing new businesses. Expectations for increased demand for building materials increased after Brazil was picked as host to the 2014 World Cup and the 2016 Olympics.

CSN expanded into the cement industry in May, opening a plant with annual capacity to produce 2.3 million tons a year using slag, a byproduct of pig iron production. The move would help the company benefit from a recovery in the economy after a short-lived recession and expected boom in infrastructure spending in the coming years.

Cimpor brings an additional 6.4 million tons a year of capacity in Brazil, which would catapult CSN into the position of the country's second largest cement producer behind Votorantim.

Cimpor has a number of large shareholders, including Portuguese construction company Teixeira Duarte with a 23 percent stake, French cement maker Lafarge with 17 percent and state-owned Portuguese bank Caixa Geral de Depositos with 9.6 percent.

The fact that the shareholding structure is fragmented is what makes this takeover bid desirable. Recent news on shareholder instability makes the timing very appropriate, said Millennium analyst Joao Mateus.

The deal requires shareholder and regulatory approval. ($1=1.787 reais) (Additional reporting by Cesar Bianconi and Alberto Alerigi Jr. in Sao Paulo; Patricia Rua, Shrikesh Laxmidas, Sergio Goncalves and Andrei Khalip in Lisbon; Editing by Toni Reinhold)

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