Senate Majority Leader Harry Reid (D-Nev.) and Sen. Joe Lieberman (ID-Conn.) have agreed that Lieberman will no longer attend Democrats’ weekly caucus lunches or the biweekly chairmen’s lunches used to formulate policy, senior Democratic aides said Tuesday.

Aides said the agreement came out of a meeting between the two, initiated by Lieberman, that occurred prior to the August recess.

A spokesman for Lieberman denied there have been any recent discussions between the Senator and Reid about his attendance at the policy luncheons and stressed that Lieberman “totally, completely of his own volition” decided he would skip certain sessions.

“Sen. Lieberman has voluntarily decided not to attend luncheons when he believes it’s likely there would be discussions of presidential politics,” spokesman Marshall Whitman said, adding that Lieberman has never been told to stay away from the luncheons.

The decision comes in the wake of Lieberman’s attacks on Democratic presidential nominee Sen. Barack Obama (D-Ill.) at the GOP convention last week, and essentially formalizes a deal Reid and Lieberman had cut earlier this year under which Lieberman would not attend meetings that included discussions of sensitive campaign or political issues.

Lieberman for weeks has voluntarily forgone the weekly caucus lunches and weekly policy lunches on Thursdays.

A Reid spokesman angrily denied that the Majority Leader had booted Lieberman from lunches.

Although Lieberman caucuses with Democrats — thus giving Reid control of the Senate — his role in the McCain campaign has increasingly marginalized his standing with his Democratic colleagues.

Lieberman’s legislative director, Joe Goffman, announced his resignation Monday. Although Goffman gave no reason for his departure, Democratic aides familiar with his decision said once work was completed on Lieberman’s climate change bill, combined with Lieberman’s convention speech, Goffman felt that it was time to move on.

Reid, Speaker Nancy Pelosi (Calif.), Democratic vice presidential nominee Sen. Joseph Biden (Del.) and other top Democrats have been increasingly vocal in their criticisms of Lieberman in recent weeks, issuing not-so-veiled threats that he could be ousted from his chairmanship of the Homeland Security and Governmental Affairs Committee in the 111th Congress.