WASHINGTON – Hillary Rodham Clinton can no longer win the Democratic nomination, Barack Obama‘s campaign said yesterday.

Obama campaign manager David Plouffe told reporters the “only way” Clinton can overcome Obama’s lead in pledged delegates after her latest lopsided defeats “is to win most of the remaining contests in blowout form.”

That’s a highly unlikely scenario that no political expert expects.

Clinton advisers were talking openly about which upcoming primary could be the final blow to her campaign.

“If she loses either Texas or Ohio, this thing is done,” Clinton adviser James Carville said on CNN last night.

But a defiant Clinton unleashed her first blistering TV attack ad against Obama yesterday and slammed him for peddling “promises.”

“I am in the solutions business. My opponent is in the promises business,” she said on a campaign swing in Texas. “I think we need answers, not questions.”

The New York senator shrugged off Obama’s Tuesday primary sweep and aides insisted the race hadn’t been decided.

“You go on,” Clinton told reporters. “Some weeks one of us is up and the other is down, and then we reverse it . . . It’s a long and winding road.”

“No one is going to be able to get the nomination without superdelegates,” said Clinton adviser Mark Penn. “We are looking at right now essentially a tied contest.”

Clinton tried to push Obama onto the defensive on health care and the economy, while her campaign focuses on a retooled strategy designed to battle Obama for delegates.

The jockeying comes as Clinton licked her wounds from three brutal losses Tuesday, in Virginia, Maryland and Washington, DC, where Obama tore into her coalition of women and working-class voters, and bested her by several hundred-thousand votes.

Clinton operatives – who once confidently predicted victory on Feb. 5 – now say the gap in delegates will be razor-thin, and that Clinton will prevail, possibly through the support of unelected “superdelegates” at the convention.

Clinton’s new TV ad, airing in Wisconsin, slams Obama for failing to agree to met her face to face in a debate there.

In the ad, which flashes images of both candidates, an announcer states that both Clinton and Obama have been invited to a debate, but only Clinton has agreed to participate.

“Hillary Clinton has said yes. Barack Obama hasn’t. Maybe he’d prefer to give speeches than have to answer questions. Like why Hillary Clinton has the only health-care plan that covers every American, and the only economic plan that freezes foreclosures.” Obama also has a housing plan, but it doesn’t include a freeze on interest-rate increases.

An Obama spokeswoman noted the candidates have had 18 debates, and said Obama’s campaign wants to “spend our time with the voters.”

Clinton agreed to an upcoming debate in Ohio on MSNBC, despite her complaints that an MSNBC correspondent accused her campaign of “pimping out” daughter Chelsea by having her appeal to delegates.

Clinton aides say she can still win the nomination by cleaning up in Ohio, Texas and Pennsylvania and prevailing at the convention this summer. But Obama is already working to sap her momentum by campaigning hard to seize a win in Wisconsin next Tuesday.

Privately, some Clinton superdelegates yesterday admitted they’re concerned about the possibility of some in their ranks flipping to Obama.

“Of course, we’re worried about it,” said one Clinton superdelegate, adding that some fellow “supers” have said they’re “depressed” by the current state of the race.

The Clinton camp announced it was hurrying to open field offices in places from Wyoming to Puerto Rico where upcoming contests will award critical delegates. But they suffered a setback yesterday when Puerto Rican Gov. Anibal Acevedo Vila endorsed Obama.

Presumptive GOP nominee John McCain slammed Obama as the Senate’s “most liberal member” and tag-teamed with Clinton’s attacks, saying Obama’s speeches were “singularly lacking in specifics.”

Additional reporting by Maggie Haberman and Carl Campanile

geoff.earle@nypost.com