WASHINGTON (CNN) -- Congress may be out of session, but Democratic staffers in the House and Senate are working this week to try and mend the differences in the two Iraq spending bills each of which calls for a withdrawal of U.S. troops, a senior Democratic aide close to negotiations tells CNN.

Although House Speaker Nancy Pelosi, D-California, hasn't named conference committee appointments yet, the Democratic aide said "it doesn't matter" noting that "everyone knows" that House Appropriations Chairman David Obey, D-Wisconsin, Rep. John Murtha, D- Pennsylvania, and Senate Appropriations Chairman Robert Byrd, D-West Virginia, will lead the negotiations.

The first step in reconciling the two bills is comparing notes to figure out major differences and points of contention, and even though lawmakers are out of town they are frequently in touch with staff by phone and e-mail.

"The timeline will be one of the last things that will get decided," this aide predicted.

Already forecasting the negotiations on the timeline, this aide notes, "It was really hard to get this bill passed the first time. If that shifts, it's going to be very difficult to pass it through the House again. How do you get language strong enough to appeal to the left, but gives enough flexibility to appeal to the right. In our language [House] we lost votes on the left. It's finding that middle ground that will work for enough people."

As for contact with the White House, the aide said they've received the message repeatedly that the current bill will be vetoed, but are making no effort to move toward discussions on a possible compromise.