Sen. Joseph I. Lieberman has talked a lot recently about the loneliness of being a pro-war independent who still sits on the Democratic side of the aisle.

But this week he will be anything but lonely — he will command center stage as floor manager of homeland security legislation (S 4, S 184) that could become a magnet for the Democratic anti-war movement.

Lieberman, elected last year in Connecticut as an independent, caucuses with the Democrats. He continues to make vague threats about joining the Republican Party, even though Republicans and Democrats say a party switch is highly unlikely. In two recent media interviews, Lieberman said he has no plans to become a Republican, but he did not rule out a switch in the long run.

A Senate Republican aide said GOP leaders have had no conversations with Lieberman about becoming a Republican and have made no special offers to lure him to their side.

Nonetheless, in a Senate where Democrats hold a 51-49 edge, even a vague hint at party-switching raises serious questions about the balance of power. If Lieberman were to become a Republican — or declare that he would caucus with Republicans while remaining an independent — the Senate would be split 50-50, with Vice President Dick Cheney casting tie-breaking votes, and the Senate could grind to a halt if Republicans insisted on re-allocating committee chairmanships and giving the GOP control of the chamber.

“Republicans can’t criticize him because they want him to jump, and Democrats can’t criticize him because they don’t want to lose the Senate,” said John Orman, a political science professor at Fairfield University in Connecticut and an outspoken critic of Lieberman. “He enjoys the attention, and he’s been working on this Sept. 11 bill for a long time. It was one of his campaign promises.”

Lieberman’s saber-rattling about party-switching — even if it’s an idle threat — gives him some leverage, even as he becomes more isolated from his party on the war. A Lieberman aide said that regardless of how the war debate turns out, there “isn’t an automatic button that would cause a switch” in party affiliation.

Democrats clearly aren’t happy with Lieberman, yet they awarded him the chairmanship of the Homeland Security and Governmental Affairs Committee. And Republicans don’t have much to offer him to induce a switch.

“He already has a substantial chairmanship. The incentives just aren’t there for him to switch,” said one former Senate aide who is now a Democratic political operative.

Majority Leader Harry Reid, D-Nev., seems not to be concerned about the latest talk of a possible Lieberman switch. He plans to entrust him with the management of the homeland security bill.

“It’s much ado about nothing,” said Reid spokesman Jim Manley, who noted Lieberman votes with Democrats on a great majority of issues, and the war is just one area where they part ways. On Senate votes in 2006 that pitted most Republicans against most Democrats, Lieberman backed the Democratic position 85 percent of the time, according to CQ vote studies.

Yet Lieberman may find himself in a unique position this week when Democrats attempt to offer an amendment that would essentially rewrite the 2002 Iraq War resolution (PL 107-243). He may be asked to add language he adamantly opposes to a bill he wants to push through the Senate.

As of Feb. 23, Democrats had not settled on their floor strategy for the homeland security bill or the Iraq resolutions. But Democratic leadership aides said Edward M. Kennedy, D-Mass., would be the party’s point man on the Iraq debate.

Jonathan Allen and Daphne Retter contributed to this story.