Deputy David Warr wants to block the sale of the old Social Security building to consider how the site could be used to benefit the community.
The government has agreed the sale of Philip Le Feuvre House and the adjoining Huguenot House for £2.3 million.
The property was marketed with a guide price of £3m to developers to turn it into 'affordable housing'.
In a report to the States, the Infrastructure Minister said the winning bid wasn't the highest of three that were made, but the higher one was judged to carry more risk.
The transaction is due to be completed by early April.
However, Deputy David Warr - who is running for Constable of St Helier in the June election - fears that the sale is being 'rushed through' before the election 'without proper scrutiny'.
He will ask the States to request the Minister defers the transaction for the next Assembly to consider 'alternatives used of the site' such as an open space or public parking.
In his request to block the sale, he says the government must recognise the wider opportunity it gives, rather than its financial value:
"We already know that we have an excess of one- and two-bedroom homes in St. Helier.
"What thought is being given to family homes, to more green space, to more play space? We know we have a mental health crisis so how does the development of this site mitigate these health issues?"
He says more discussions should be had on how to optimise the value of a key site in town.
"If ultimately the sale to a property developer is proven to be the correct one, then so be it, I simply ask that we just take a moment to look at the wider utility to our community."
Parliament has until the end of 2 April to conclude any business before the pause for the general election on 7 June.
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