Top Republican John Boehner and leading Democrat Harry Reid are tweaking their budget plans after nonpartisan analysts said their sums did not add up.
The US Congressional Budget Office (CBO) said neither Mr Boehner's plan nor Mr Reid's would cut the deficit by as much as they had both estimated.
House Republicans have been meeting behind closed doors to discuss the Boehner plan.
Mr Reid said Mr Boehner's proposal could not pass the Senate.
The US runs a budget deficit that topped $1.5tn (£920bn) this year, and has amassed a national debt of $14.3tn.
'No off-ramps'
Lawmakers have been locked in weeks of bitter negotiations over raising the US borrowing limit by the deadline of 2 August.
The bill proposed by Mr Boehner was being rewritten on Wednesday after the CBO said it would cut spending less than had been advertised - about $850bn over 10 years, rather than $1.2tn.
Republicans planned a House vote for Thursday on the reworked plan.
Mr Reid's office told the BBC the Senate majority leader was also revising his plan after the CBO said the proposal would cut $2.2tn from deficits, about $500bn less than had been claimed.
Mr Reid has not said when his bill would reach Congress for a vote.
The White House warned on Wednesday that time was quickly running out to reach a compromise on the US debt limit.
"That deadline is hard and fast," White House spokesman Jay Carney said of next Tuesday's expiry date on the debt ceiling.
"People keep looking for off-ramps. They don't exist," he added.
http://www.bbc.co.uk/news/world-us-canada-14318377
Note: Update Record,27 July 2011 Last updated at 19:14 GMT