The registry recently raised its fees, blaming a recession-hit income
The Land Registry wants to axe 1,500 posts - about 25% of its workforce - as part of a five-year plan to cut costs.
The registry believes the closure of offices in Croydon, Peterborough, Portsmouth, Stevenage and Tunbridge Wells will also help save £92m a year.
The proposals will make the registry "fit for the future", it says.
The Public and Commercial Services (PCS) union said the proposals had left staff "shocked and angry", and that the plans could damage services.
A statement on the Land Registry website said the "reorganisation and transformation... will cut its costs significantly and put it in the best possible position to deliver the services its customers demand".
The government body, which registers all land ownership transactions in England and Wales, is funded by fees charged for its services and receives no taxpayers' money.
The property market downturn in the recession led to a loss in 2008-9, with another loss predicted this year.
But the consultation document on the proposals says that "although recent events have seriously affected Land Registry the current proposals are consistent with the trends in recent years".
"The changes will help create a Land Registry that is fit for the future, that can live within its means and that can continue to provide an outstanding service to its customers," a statement on the registry website said.
"Having looked at a range of possibilities, it is proposing to close five local offices and to reduce staff numbers to reflect the move to more online services and the impact of internal efficiency measures."
Based on current and anticipated levels of business coming into the Land Registry, it estimates that it needs just 4,500 of about 6,000 current full-time positions.
It also announced plans to outsource some "support functions" and sell surplus property.
Two offices in Plymouth, where about 800 people are employed, are due to be merged.
'Shocked and angry'
In the consultation document, chief executive Peter Collis wrote: "The proposed closure of offices will be very unwelcome news for our staff and we are determined to do all we can to ameliorate the impact on our exceptionally loyal, dedicated and hard-working workforce.
"However we believe these measures are necessary if we are to become the smaller, leaner, more flexible organisation we need to be."
PCS general secretary Mark Serwotka said that the announcement had left staff "shocked and angry".
"With 1,700 jobs already gone, there is a real danger that services to the public will suffer as the agency is cut to the bone," he said.
The union believes 1,100 jobs could be lost with the office closures, while a further 400 staff in human resources, facilities and 14 regional file stores in England face privatisation.
"Experience shows that privatisation isn't the silver bullet to save costs and often provides poor value to the taxpayer with corners cut in a bid to turn in a profit," Mr Serwotka said.
"The government needs to recognise that putting hard-working civil and public servants on the dole at a time of economic uncertainty will only prolong the recession and the communities affected."
Public consultation has been launched on the planned office closures, ahead of final decisions due to be made in February next year.