Senate leaders on Monday were optimistic that they could broker a deal that would avoid the U.S. default on its debt and reopen the government, perhaps before the afternoon meeting the four top congressional lawmakers have with President Obama.

Senate Majority Leader Harry Reid, D-Nev., and Minority Leader Mitch McConnell, R-Ky., were huddled most of Monday in McConnell's office, working out a deal that would raise the nation's debt ceiling and reopen the government. The leaders were making enough progress that Obama postponed their afternoon meeting at the White House to give them more time to work it out.

While both leaders were tight-lipped on the details of those talks while they shuffled between the Senate floor and McConnell's office, they remained upbeat.

McConnell said the negotiations have been "very useful."

"We're optimistic we're going to be able to come together and get an outcome," McConnell said.

Reid and McConnell only spoke for the first time Saturday, and much has been written in the last 24 hours on the strained relationship between the two long-time party stalwarts. But Reid called those reports exaggerated and said he would like to have the framework of a deal done before Reid and McConnell join House Speaker John Boehner, R-Ohio, and Minority Leader Nancy Pelosi, D-Calif., at the White House.

The final outcome between Senate leaders could put House Republicans in a tough situation. If they block a bipartisan agreement worked out by Reid and McConnell, public blame for the government's default on Thursday could fall squarely on the heads of the GOP.

"I'm very optimistic we will reach an agreement that is reasonable in nature this week," Reid said.