(Adds details from central bank)
TRIPOLI, Dec 8 (Reuters) - Libya's budget income fell to around $15 billion in the period from January to November from $45 billion a year before, the central bank said on Monday.
In a statement, it blamed the 40 percent fall in oil prices since June and the state's inability to collect customs duties.
Expenditure in the period was 38.5 billion Libyan dinars ($30 billion). The bank warned the tumble in income was affecting foreign currency reserves, which it has used in the past to cover deficits, but did not elaborate.
Reserves were around $109 billion at the end of June, according to the most recent data.
The central bank has tried to stay out of a political struggle between two rival factions threatening to tear apart the OPEC member country three years after the fall of autocrat Muammar Gaddafi.
Libya has two governments and parliaments since a group called Libya Dawn seized the capital, setting up its own cabinet and forcing the recognized prime minister to move to the east.
Mostly comprising salaries for civil servants and subsidies for wheat and other basics, budget spending is hard to cut.
Expenditure on salaries stood at 21.1 billion dinars in January-November, while subsidies made up 12.7 billion dinars, the central bank said.
Reporting by Ulf Laessing; Editing by Patrick Markey and Catherine Evans