Vice President Biden and Sen. Mitch McConnell were locked in urgent talks late Sunday over the “fiscal cliff” after Democrats offered several significant concessions on taxes, including a proposal to raise rates only on earnings over $450,000 a year…

They also relented on the politically sensitive issue of the estate tax, according to a detailed account of the Democratic offer obtained by The Washington Post, promising to stage a vote in the Senate that would guarantee that taxes on inherited estates remain at their current low levels, a key GOP demand.

Still, McConnell (R-Ky.), the Senate minority leader, was holding out to set the income threshold for tax increases even higher, at $550,000, according to people close to the talks in both parties. And he was protesting a Democratic proposal to raise taxes on investment profits for households with income above $250,000.

The two sides were also sharply at odds over automatic spending cuts set to decimate budgets at the Pentagon and other federal agencies next month.