Story highlights Estimates for President Donald Trump's wall have ranged in the tens of billions

But the supplemental only sets aside $1 billion for the wall

Washington (CNN) The Trump administration is planning to ask for a relatively small amount of money to start building the President's long-promised border wall this year -- far short of estimates of what the wall might cost, according to preliminary numbers shared with CNN.

Despite President Donald Trump's repeated calls to begin immediately building a substantive wall along the entire Southern border, which experts say would cost tens of billions of dollars, the administration is not asking for even a fraction of that in the near-term.

Congress is preparing to receive a request from the administration on March 16 for supplemental funds for fiscal year 2017, according to two sources familiar with the timing, along with an overall budget request for fiscal year 2018. Office of Management and Budget Director Mick Mulvaney previously said the supplemental request, which will also include defense spending, will total $30 billion.

But according to preliminary numbers shared with CNN by a source familiar with the proposal, only $6.6 billion of the supplemental budget request will go toward border security -- and just $1 billion of that will be for the wall.

The source referred to the money as a "down payment" of sorts, with more to be allocated later.

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