(Recasts first sentence with forecast of steel prices, adds comment by chief executive, financial details, closing share price)
SAO PAULO, Oct 26 (Reuters) - Brazilian steelmaker Usinas Siderurgicas de Minas Gerais SA (Usiminas) on Friday forecast stable steel prices in the final three months of the year, following a 10 percent rise in the third quarter.
Rising steel prices, along with a currency boost for exports, boosted quarterly profit at Usiminas to 289 million reais ($79 million), almost four times higher than a year earlier, topping the Refinitiv average estimate of 188 million reais.
"Our forecast ... for the fourth quarter will be to maintain prices at the current level," Usiminas' chief executive, Sergio Leite, told analysts on a conference call.
Shares of Usiminas closed 1.6 percent higher at 10.06 reais on Friday after rising as much as 3 percent after the results were released.
"The operational results were strong in all aspects, with higher prices and higher volumes in the domestic market," brokerage XP Investimentos wrote in a note to clients.
Usiminas sold more than 85 percent of its steel in the local market. Overall production was 1.1 million tons of steel, a 9 percent increase from 2017, and higher steel prices boosted revenue by much more. Year-over-year revenue increased by 40 percent to 3.4 billion reais.
Company executives said on the conference call they expected to maintain steel prices around the same levels during the rest of the year, although they were renegotiating prices with the auto industry, a big customer.
An explosion in a gasometer in Usiminas' Ipatinga plant, which injured more than 30 people, did not affect production, the company said, but it drove production costs up by some 47 million reais.
"The preliminary report of investigation concluded that the cause of the explosion was the undue entry of atmospheric air in the gasholder," Usiminas said in the filing.
Since Usiminas is not a major exporter of steel to the United States it is not expected to be hurt by U.S. President Donald Trump's new tariffs. Trump has put in place tariffs on imports of Chinese steel and capped imports of Brazilian steel.
Leite said the world had turned protectionist since Trump was elected and hinted that Brazil should take measures to protect its own industry if necessary.
"We are liberals, we are in favor of free trade, but it needs to reach an equilibrium," he said. ($1 = 3.6720 reais) (Reporting by Marcelo Rochabrun in Sao Paulo Additional reporting by Alberto Alerigi Jr. and Tatiana Bautzer in Sao Paulo Editing by Susan Thomas and Matthew Lewis)