WASHINGTON (Reuters) - The U.S. Congress, when it moves at all, moves slowly. But when its back is against the wall, as it will be on any deal to resolve the year-end "fiscal cliff," it can be very efficient.
For example, barely two days separated the announcement of a deal on the debt ceiling on July 31, 2011, and its enactment on August 2.
That required limits on the time for debate and a ban on amendments, which in turn required solid support from the leadership of both parties.
Realistically, aides on Capitol Hill estimate that if President Barack Obama reaches a deal with Republicans on avoiding the fiscal cliff, it could take about a week for specialists in Congress to translate the pact into legislation and for the House of Representatives and Senate to then vote on it.
Republican House Speaker John Boehner is in negotiations with the White House on deficit-reduction ideas that would replace $600 billion in potentially devastating tax increases and spending cuts that are scheduled to begin in January.
An impasse between the two showed signs of improvement over the weekend after Boehner indicated a willingness to allow income tax rates to rise on the richest Americans - those with net incomes above $1 million a year - as part of a deficit-reduction deal.
Obama has insisted on the tax rate hike as a necessary first step before progress could be made on long-term spending cuts, but the president was seeking a lower, $250,000-a-year threshold for raising income taxes.
The speed with which Congress could act on a deal - mindful of the December 31 deadline it faces - will depend on the scope and complexity of the agreement reached by Obama and Boehner.
The more complex the deal, the longer it will take to draft. For example, if a complicated "framework" is included instructing Congress to take specific steps next year, that could add to the time it takes to write the legislation. This is especially true if it includes an enforcement mechanism - a trigger like automatic spending cuts - aimed at pressuring lawmakers to actually follow through next year.
"I think the goal is to get a deal before Christmas," a senior House Republican aide said, adding it may take until New Year's Eve to get it ready for a vote by the House and Senate.
A senior Senate aide speculated that it would take three to five days to transform a deal into legislative language - the bills that would be debated in the two chambers.
"From handshake to vote, the quickest possible would be five to six days" for passage, the aide said.
Once a bill or bills are written, the aide said the Congressional Budget Office and the Joint Committee on Taxation would have to review the provisions to determine whether they actually would achieve the goals that were intended.
For example, the CBO would review any spending cuts contained in the deal and "score" their savings and impact on budget deficits. The same for the Joint Committee's assessment of any revenue increases.
Once CBO and the Joint Committee "scores" are in place, the legislation technically would be ready to move to the House and Senate floors. Measures that contain tax changes, which this deal is expected to have, technically must be approved first by the House, but there are ways around that requirement if leaders see the need.
A House rule requires that once legislation is publicly posted, it must wait 72 hours before being debated on the House floor.
During that time, Boehner and his leadership team would spend many hours rounding up the votes for passage. If it looked as if the measure was going to fail, they could either postpone the House debate or try to alter the deal to win more support.
In the Senate, there are plenty of delays that individual senators could erect if they wanted to slow down the bill.
Those roadblocks could require that the Senate muster at least 60 votes in the 100-member chamber for the legislation to move to debate and then votes on passage.
Any changes that either chamber were to make to the measure through amendments could also complicate matters. Once the deal is reached, however, leaders would work hard to avoid controversial amendments that could make everything fall apart.
If the House and Senate do manage to pass the legislation, Obama likely would act quickly to sign it into law, racing against the December 31 deadline.
There was no better example than August 2011, when Obama signed a deficit-reduction and debt-increase measure just before the country was set to default.
If the Obama-Boehner negotiations bog down but eventually succeed, it is possible that the legislation would not be voted on until the first week of 2013.
Last week, Representative Steny Hoyer, the second-ranking Democrat in the House, floated the possibility that if there was an agreement in principle by year's end, Congress could extend current tax and spending rates for a couple of weeks to provide more time to actually pass the new regime into law.
Additional reporting by Thomas Ferraro; Editing by Fred Barbash and Eric Beech