The government has angered environmentalists and many Venetians by rejecting alternatives to the costly flood barrier system being built to protect the sinking city from high tides.
Public Works Minister Antonio Di Pietro on Friday presented a report to the cabinet, saying that different proposals tabled by Venice's city council were little different from ideas discarded 25 years ago.
"There are no new elements which make it necessary to modify the work under way on the Moses system," he said.
After 30 years of debate and testing, work began on the 'Moses' flood barriers in 2003. Completion is scheduled for 2012, by which time at least 3.5 billion euros will have been spent on the project.
The city's mayor, Massimo Cacciari, has called for a rethink of the project. It is opposed by environmentalists worried about the impact of the system on the lagoon's ecosystem and by many Venetians who argue that the money could be spent on cheaper, less complex solutions.
But Di Pietro said the solutions proposed were inadequate and the environmental impact of the work done on Moses over the last three years had been minimal. He also said the .
His report was approved by the cabinet, but with three of its members - including Environment Minister Alfonso Pecoraro Scanio - voting against.
The green light means that when government representatives meet engineers and local administrators in coming weeks to discuss the project they will demand that the construction work continue as planned.
"This is a mistake," said Pecoraro Scanio, who is leader of Italy's Green party. "There are cheaper and more useful alternatives for dealing with high tides".
Moses consists of 79 hollow metal barriers into which air can be pumped in order to make them rise from the seabed and so block the three channels linking the lagoon to the Adriatic Sea when high tides are forecast.
Among the ideas put forward by Venice's administrators are underwater dams with movable sections and barriers which could be slid into place using a crane-type apparatus on each side of the channels.
"I don't see why the government insists on charging ahead, even at the cost of an internal split," said Roberto della Seta, head of environmental lobby Legambiente.
He said the alternatives put forward had not been given a fair hearing.
Meanwhile, the centre-right president of the Veneto region, who is a supporter of the Moses project, thanked the centre-left government for its commitment to "safeguarding Venice".
Flooding is a constant problem for Venice and the picturesque St Mark's Square is covered with water dozens of times every year. According to experts, Venice is increasingly subject to flooding for three reasons: the lagoon floor is rising because of incoming silt; the extraction of methane gas in the sea off Venice causes its islands to sink; and sea levels are rising in general because of global warming.
