One change Obama has proposed would tighten the adjustment for inflation of benefits such as Social Security, meaning annual increases for future recipients would grow at a slower pace.

Opponents of the reform, known as "chained CPI" in reference to the consumer price index it involves, argue it hurts vulnerable senior citizens and others who most need their benefits.

If achieved, a grand bargain would give Obama a major political victory and a boost in cementing his desired presidential legacy after the controversial health care and Wall Street reforms of his first term.

Republicans also would get credit from moderates and independents for a willingness to compromise, but conservatives could punish them with primary challenges in 2014 and beyond.

Another possible outcome is a limited agreement that would include some elements under discussion.

For example, a smaller agreement might end some tax breaks and loopholes while cutting Medicare costs paid providers, not beneficiaries, to achieve $500 billion or so in deficit reduction over 10 years.

Such a result, coupled with previous spending cuts and the January fiscal-cliff deal, would fail to reach the total $4 trillion in deficit reduction over the next decade that economists and political leaders have targeted as the minimum amount needed.

It also would allow both parties to simultaneously claim credit for making some progress after the past years of dysfunction while continuing to blame the other for preventing more.

A status quo outcome of no major deficit reduction steps would mean continued brinksmanship over each pending fiscal deadline, as well as further economic uncertainty that already has lowered the U.S. credit rating and slowed growth.