(Adds context, additional detail on year-to-date deficit)
BRASILIA, Aug 27 (Reuters) - Brazil's central government posted a primary budget deficit of 7.224 billion reais ($2.04 billion) in July, the third straight monthly gap as the government struggles with plummeting revenues, according to Treasury data released on Thursday.
The central government account covers federal ministries, the central bank and social security.
July's primary budget balance, which excludes interest payments, was the worst on record for the month and followed a primary deficit of 8.2 billion reais in June.
A sharp drop in tax revenues as the economy contracts has forced President Dilma Rousseff to slash the public sector's primary surplus targets for this year and the next two years.
Her struggles to rebalance public accounts after years of heavy spending during her first term have raised the probability that the once-promising economy could lose its investment-grade rating next year.
In the year through July, the central government has accumulated a deficit of 9.05 billion reais, the Treasury said.
The 2015 central government primary surplus target was cut last month to 5.8 billion reais, or the equivalent of only 0.1 percent of gross domestic product, from 55.3 billion reais originally.
Many economists believe the government will fail to reach its new goal and record a deficit this year as the downturn has turned out to be deeper than what most had expected.
$1 = 3.54 Brazilian reais Reporting by Luciana Otoni; Editing by Bernard Orr