FARMINGTON, Conn. — The passion and energy fueling the antiwar challenge to Sen. Joseph Lieberman in Connecticut's Senate primary signals a power shift inside the Democratic Party that could reshape the politics of national security and dramatically alter the battle for the party's 2008 presidential nomination, according to strategists in both political parties.

A victory by businessman Ned Lamont on Tuesday would confirm the growing strength of the grass-roots and Internet activists who emerged in Howard Dean's presidential campaign. Driven by intense anger at President Bush and fierce opposition to the Iraq war, they are on the brink of claiming their most significant political triumph, one that would reverberate far beyond the borders here.

An upset by Lamont would affect the political calculations of Sen. Hillary Rodham Clinton, D-N.Y., who like Lieberman supported giving Bush authority to wage the Iraq war, and could excite interest in a comeback by former vice president Al Gore, who warned in 2002 that the war could be a grave strategic error. For at least the next year, any Democrat hoping to play on the 2008 stage would need to reckon with the implications of Lieberman's repudiation.

Even backers of the 2000 Democratic vice presidential nominee are now expecting this scenario. Two public polls in the past three days show Lamont with a lead of at least 10 percentage points.

While there are reasons beyond Lieberman's strong support for the war and what critics say is his accommodating stance toward Bush that have put him in trouble, the results will be read largely through the prism of what they say about Iraq and Bush's popularity.

The full ramifications of a Lieberman defeat are far from certain. One may be to signal immediate problems for Bush and the Republicans in November, but another could be to push Democrats into a more partisan, anti-war posture, a prospect that is already adding powerful new fuel to a four-year-long intraparty debate over Iraq.

Strategists say the Connecticut race has rattled the Democratic establishment, which is virtually united behind the three-term incumbent's candidacy.

"This sends a message to all Democratic officeholders," said Robert Borosage of the liberal Campaign for America's Future. "You're going to have a much tougher Democratic Party."

That could be felt most acutely by Clinton, who polls show is the early front-runner for the 2008 nomination and who has drawn criticism from the netroots activists for opposing a timetable for withdrawal. Clinton appears to have gotten the message, as she demonstrated with sharp questioning of Defense Secretary Donald Rumsfeld at a Senate hearing last Thursday.