Failure by the Congress to pass a tax cut deal soon would materially increase the risk of the economy stalling and a double dip recession, White House economic adviser Larry Summers said on Wednesday.

Summers, who is leaving his post as Obama's top economic adviser this month, said Obama's deal with Republicans to extend Bush-era tax cuts for the middle class and the wealthiest Americans would provide more fiscal support for the economy than most observers expected only weeks ago.

Failure to pass this bill in the next couple weeks would materially increase the risk that the economy would stall out and we would have a double-dip, Summers told reporters at the White House.

As much as we regret the elements in it that do not seem to us to be a good use of public resources, on balance the benefits to the economy make this a very worthwhile deal, he said.

The deal includes a continuation of unemployment insurance -- a key White House demand.

Summers said the president wanted to continue the popular Build America Bonds program this year or next year.

He'd like to see them go forward, Summers said.

Republicans have said they will block the program in their tax deal with Obama. White House spokesman Robert Gibbs said it was not currently part of the deal.

(Reporting by Jeff Mason and Ross Colvin; Editing by Doina Chiacu)