* Lula field decline leads to drop in subsalt output
* Subsalt losses wipe out rebound in Roncador field
* Weak output to crimp gov't tax revenue as oil price falls
RIO DE JANEIRO, Dec 2 (Reuters) - Brazil's oil output was little changed in October compared with September as production from the country's largest offshore subsalt fields fell, erasing gains from older fields ramping up output following maintenance, the country's oil regulator said on Wednesday.
Brazil produced 3.02 million barrels a day of oil and natural gas equivalent (boepd) in the month, 0.3 percent more than the previous month, ANP said.
The figures are seen as bad news for the government of President Dilma Rousseff, which is struggling to maintain tax revenue with the economy immersed in its deepest recession in 25 years.
Production in Brazil is less than two-thirds of the more than 5 million barrels a day (bpd) her government once said Brazil would be producing by now, limiting the giant royalty payments she promised would pay for healthcare and education.
World oil prices have also fallen to seven-year lows, limiting taxes on the crude Brazil produces. Output likely fell again in November after Petrobras suffered its worst strike in 20 years.
Declines in the Lula field, operated by state-run Petroleo Brasileiro SA in partnership with Britain's BG Group Plc and Portugal's Galp Energia SGPS SA, as well as reduced output from Royal Dutch Shell Plc areas negated the impact of a surge in output from Petrobras' Roncador field.
Output in the Lula field fell 5.2 percent to 331,000 bpd in October from 349,000 bpd in September, according to ANP data. Roncador rebounded, jumping to 320,000 bpd, up 26 percent from 254,000 bpd in September. The two fields have been the country's top two producers for some time.
Overall oil and natural gas output from the subsalt, an offshore region south and east of Rio de Janeiro where oil is trapped far beneath the seabed by a layer of mineral salts, fell for a second straight month, dipping 2.3 percent to 1.01 million boepd from 1.03 million boepd.
Output rose 1.5 percent from a year earlier, meaning new subsalt output is only barely keeping up with declines from the so-called old giants in the Campos Basin, which at 65 percent of Brazil's output, is still the country's most productive region.
Petrobras remained the largest producer in Brazil in October with 2.50 million boepd, or 83 percent of Brazil's total production.
BG was the No. 2 producer with 181,372 boepd, or 6 percent of production. BG's October output fell 2.7 percent from September. (Reporting by Jeb Blount, editing by G Crosse)