Brazil's Federal Court of Accounts (TCU) said only 5 percent of a planned 1.67 billion Brazilian reals ($746 million) had been spent in a three-year period ending in 2012.
Rio organizers estimated in bid plans submitted in 2009 that 1.67 billion reals would be spent on projects by the end of 2012.
The slow start has worried International Olympic Committee inspectors, who have warned several times including during a visit a month ago that preparations are behind schedule.
The IOC has blamed it partly on a lack of cooperation among various levels of government.
Rio officials have also been criticized for not announcing a budget, which is expected in the next few months.
Officials have acknowledged $700 million in public money may be needed to cover a shortfall in the operating budget.
The operating budget money to run the games and not to build infrastructure was listed at $2.8 billion in the original bid document. That number is expected to rise to between $3.5-4 billion.
The cost of the Olympics and the 2014 Brazil World Cup are under heavy scrutiny at home.
Protests in June during the Confederations Cup a warm-up for the World Cup focused on Brazil's poor schools, run-down hospitals and social inequality, contrasted with multi-billions being spent on mega-sports events.
Brazil is spending about $13.3 billion of largely public money to stage the World Cup. Public spending on the Olympics is expected to equal that of the World Cup or exceed it.
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