Speaker Nancy Pelosi (D-Calif.) lashed out at Sen. Joe Lieberman (ID-Conn.) Wednesday for his “irresponsible” attacks on Sen. Barack Obama (D-Ill.) and said the comments could endanger his position in the Senate next year.

Pelosi is the highest-profile Democrat to attack Lieberman, who has enjoyed a protected status of sorts because Senate Majority Leader Harry Reid (D-Nev.) needs him to keep the Senate in Democratic hands. Lieberman, a supporter of Sen. John McCain (R-Ariz.), said this week that Obama was unfit to be a wartime president.

Speaking on KGO radio in San Francisco, Pelosi suggested Democrats would not forget his transgressions come November.

“Joe Lieberman has said things that are totally irresponsible when it comes to Barack Obama. Here we have a leader for the future, really a great leader for the future,” Pelosi said, adding that Republicans have used Lieberman because he is “one of their best weapons, of course, [and] is someone who is considered by some to be a Democrat.”

Pelosi went on to note that Democrats are expected to bolster their Senate ranks next year, which could marginalize Lieberman.

“The Democrats in the Senate are in a tough spot. They have 51 votes. Joe Lieberman organizes with them. In 85 days or something, they will have five more Democrats. They won’t need him to make the majority. And it will be interesting to see what the leadership in the Senate, the Democratic leadership in the Senate, does at that point in terms of Joe Lieberman’s chairmanship of his committee,” she said. Lieberman is chairman of the Homeland Security and Governmental Affairs Committee.

Although Pelosi will have no role in how Senate Democrats organize themselves next year, she is close to Reid and her warnings could carry more weight than the venting of other Democrats.

The San Francisco Chronicle first reported Pelosi’s comments.