UPDATE 1-Brazil Gerdau Q3 net tumbles 54 pct from year ago

* Net income tumbles 54 pct on year-on-year basis (Recasts with year-on-year figures from last year's release)

SAO PAULO, Nov 5 (Reuters) - Gerdau (GGBR4.SA)(GGB.N), Brazil's largest steelmaker, reported on Thursday net income of 655 million reais ($378 million) for the third quarter, a 54 percent drop from a year ago as revenue almost halved.

The company did not provide comparable year-on-year figures in a securities filing. A previous release from Dec. 8, 2008 had net income of 1.42 billion reais for the third quarter of last year.

Gerdau was expected to report a third-quarter profit of 677 million reais, according to the average estimate of six analysts in a Reuters poll.

Gerdau, which is based in the southern Brazilian city of Porto Alegre, posted a loss of 329 million reais in the second quarter after a massive asset write-down that topped 1 billion reais.

Net revenue was 6.81 billion reais in the three months ended on Sept. 30, compared with 12.44 billion reais a year earlier and 6.40 billion reais in the second quarter.

Cost of sold goods was 5.30 billion reais, compared with 8.35 billion reais a year earlier, reflecting idle capacity at some of the company's mills in Brazil, the United States, Europe and Latin America.

Costs fell from 5.60 billion reais in the second quarter.

Earnings before interest, tax, depreciation and amortization, a measure of operational profitability known as EBITDA, came in at 1.38 billion reais in the third quarter. It was 3.84 billion reais in the year-earlier period and 595 million reais in the second quarter of this year.

EBITDA as a proportion of revenue, the so-called EBITDA margin, was 20.2 percent, compared with 30.9 percent a year earlier and 9.3 percent in the prior three months.

($1=1.733 reais) (Reporting by Guillermo Parra-Bernal; Editing by Derek Caney, Dave Zimmerman)