A breakdown in negotiations could also ignite turmoil in financial markets, Vitner said. It could resemble the 700-point fall in the Dow Jones industrial average in 2008 after the House initially rejected the $700 billion bailout of major banks.
Since President Barack Obama's re-election, nervous investors have sold stocks. The Standard & Poor's 500 index sank 2.3 percent last week, its worst weekly drop since June. The sell-off resulted in part from anxiety over higher tax rates on investment gains once the fiscal cliff kicks in.
Last week, Obama said he was open to compromise with Republican leaders. But the White House said he would veto any bill that would extend tax cuts on income above $250,000.
Republican House Speaker John Boehner countered that higher tax rates on upper-income Americans would slow job growth. Boehner argued that any deal must reduce tax rates, eliminate special-interest loopholes and rein in government benefits.
More than 50 percent of the tax increases would come from the expiration of tax cuts approved in 2001 and 2003 and from additional tax cuts in a 2009 economic stimulus law.
The first set of tax cuts reduced rates on income, investment gains, dividends and estates. They also boosted tax credits for families with children. Deductions for married couples also rose. The 2009 measure increased tax credits for low-income earners and college students.
About 20 percent of the tax increase would come from the expiration of a Social Security tax cut enacted in 2010. This change would cost someone making $50,000 about $1,000 a year, or nearly $20 a week, and a household with two high-paid workers up to $4,500, or nearly $87 a week.
The end of the Social Security tax cut isn't technically among the changes triggered by the fiscal cliff. But because it expires at the same time, it's included in most calculations of the fiscal cliff's effects.