WASHINGTON (Reuters) - Here is what is happening on Monday as lawmakers prepare to vote on a deal to raise the $14.3 trillion limit on U.S. borrowing, just a day before the deadline to avert an unprecedented default.

* The White House and some congressional leaders start the process of selling the debt deal to rank and file. Both the right and left grumble about the details.

* Vice President Joe Biden meets separately with Senate and House Democrats. Says following the meetings that he is confident the legislation will pass.

* Senate Minority Leader Mitch McConnell following a meeting with his fellow Republicans says he "is very optimistic" that the deal will pass.

* Representative Raul Grijalva, who heads a group of liberal Democrats in the House, tells Reuters Insider he expects most members of his progressive caucus, which has about 75 members, to vote against the bill.

* House Minority Leader Nancy Pelosi tells her fellow House Democrats to vote their conscience on the deal, but keep in mind the consequences, Democratic members tell reporters following a closed-door meeting of House Democrats.

* The House is expected to vote on the bill on Monday evening. Senate Majority Leader Harry Reid says he hopes to schedule a Senate vote on Monday or Tuesday at the latest.

* The Business Roundtable, which represents some of the biggest U.S. companies, urges Congress to act immediately and pass the debt limit bill.

* The White House declines to comment on how credit rating agencies will judge the debt deal.

* U.S. stock prices surge as Wall Street opens for trading. But they turn negative as investors worry there might not be enough support in the Republican-led House for passage and after poor manufacturing data.

(Reporting by Donna Smith; editing by Mohammad Zargham)