Republican and Democratic negotiators careened toward a mid-afternoon deadline for a "fiscal cliff" deal, still uncertain they can come up with a deal to avoid the fiscal cliff that can pass both the House and Senate and win President Obama's signature.

Focused on the Senate, which would act first, the negotiations involve setting a threshold for income tax rate hike at $400-500,000 incomes — higher than Mr. Obama wants but near the last offer he made to House Speaker John Boehner before their talks collapsed earlier this month. One participant in the discussions said rates on both capital gains and dividends would rise to 20% from 15% currently in their potential deal.