MANCHESTER, N.H. — Senator Clinton can expect a significant challenge in the 2008 presidential primary here if Senator Obama decides to launch his own campaign.

That was the indication from Mr. Obama’s appearance here yesterday, when he brought a crowd of 1,500 Democratic activists at the Armory Convention Center to their feet.

Mr. Obama did not criticize Mrs. Clinton directly. But he offered language — “something different,” “something new,” “America is ready to turn the page” — that at least some in the audience understood as drawing a distinction between the two Democratic senators, one from New York, and one from Illinois.

Mr. Obama invoked his pastor, as well as virtue, energy independence, and democratic engagement — with a notable small d.

“I actually think that the reason I’m getting so much attention right now is that I’ve become short-hand … for a spirit that the last election we went through represented,” Mr. Obama said. “We are looking for something different. We are looking for something new. We are going to re-engage in our democracy in a way we haven’t done in a long time. We are going to take control of our collective lives together.”

Mr. Obama largely avoided talk of his potential opponents in a 2008 New Hampshire race, but his touchy-feely, nonconfrontational rhetoric, in and of itself, sent a powerful message to Democrats. He will not give them the robotic, scripted sound-bites of his most serious opponent, Mrs. Clinton. He will campaign as a celebrity-prophet, brandishing his two memoirs and a biography heavy on community organizing. His 2008 effort is shaping up as the perfected form of the campaign Senator Bradley of New Jersey attempted to run in 2000 and Governor Dean attempted with more success in 2004.

The speech to the large and energetic crowd was more than an opportunity to appear on local New Hampshire television. Mr. Obama also drew a press contingent of a size more often seen in the few months before the primary election, not more than a year prior. About 150 print and television reporters were on hand, including such national political bigfoots as Adam Nagourney of the New York Times and Jonathan Alter of Newsweek.

Many of the non-reporters in the crowd were the kind of volunteers and organizers that form the backbone of a primary field organization. An operative filled a legal pad with the contact information of enthusiastic attendees who lined a rope line following the event waiting for a chance to meet Mr. Obama. Such a list is a treasure trove for a candidate trying to build an organization.

The mood surrounding a run by Mr. Obama is rapidly approaching that of hysteria. If he jumps into the race and Senator Clinton goes ahead with a presidential run, the contest in New Hampshire could rapidly become a two-candidate race.

The more Mr. Obama says in his nonpartisan, inoffensive, some would say “inspiring,” way, things such as “America is ready to turn the page…This is our time…A new generation is preparing to lead,” as he did last night, the more he is saying, in effect, listen to me, I’m not Senator Clinton.

That’s, at least, how many attendees heard it. They responded to his new-sounding language.

“It was inclusive. He talked about America, not party,” said John Decker of Stratham, N.H., as he waited along a rope-line for Mr. Obama to approach. Asked to compare Mr. Obama with Mrs. Clinton, he said, “he has much more charm and panache. He has all the things Hillary’s husband has.”

Queried similarly, Jaime Contois, a Keene-based community organizer, said: “He’s based on a very deep spiritual connection. His passion runs deeper than party.”

Ned Helms of Concord, a veteran of Democratic politics who served as state party chairman between 1990 and 1992, called Mr. Obama’s remarks “very heartening.” Choosing his words carefully, he said “the reality is Barack Obama is who he is. You can’t talk yourself or buy yourself into being a new face.” He added that he was leaning between supporting Mr. Obama or Vice President Gore, should he run.

Mr. Obama, 45, is a graduate of Harvard Law School and would be the first black president of America. Mrs. Clinton, 59, is a graduate of Yale Law School and would be the first female president of America. Mrs. Clinton grew up in Illinois, the state Mr. Obama has represented in the Senate since 2004.

That the event was something special for New Hampshire was evident before it even began. The line of the 1,500 Democratic activists awaiting entry to the event wound through the lobby, past the hotel restaurant, by the pub in which a handful of souls watched the New England Patriots, into the vacant space of the Manchester Convention Center.

“I have never seen as big a crowd as this, this early in the primary season,” said a principal of the Dewey Square Group, a lobbying and communications firm, Charles Campion. Mr. Campion, a former aide to Governor Dukakis of Massachusetts, has seen his share of primary fights in New Hampshire. Mr. Campion said he is currently supporting Senator Kerry.

The setting for Mr. Obama’s speech yesterday was the same place Mr. Kerry addressed successfully in October. The environment in New Hampshire has entirely shifted since then. Should Mr. Kerry not seek the presidency, a race akin to the American and Soviet effort to scoop up German scientists will surely ensue to sign up his strategists, operatives and supporters.

In his remarks, the governor of New Hampshire, John Lynch, compared the frenzy over Mr. Obama to a rock star. He said, “We originally scheduled the Rolling Stones…We cancelled them when we realized Senator Obama would sell more tickets.”