The raucous scene at a University of Miami tailgate party on a recent weekend might have seemed an unlikely spot for a debate over Obamacare. But with six dozen pizzas in hand, the youthful staffers from Generation Opportunity rolled up in Hummers and Ford F-150s to claim their spot.

With "DJ Joey" spinning electronic dance beats, the group lured Miami's revelers to their tent with beer pong tables and plenty of swag, including bottle openers and beer cozies bearing the group's logo on a black-and-white pill capsule: "Opt Out."

They were seeking to keep out of President Obama's healthcare plan a group that, more than any other, must be in the program for it to succeed. Eighteen- to 34-year-olds, that demographic group courted relentlessly by television advertisers and presidential candidates, are needed in the insurance exchanges to offset, with their youth and health, the pool of older and sicker Americans expected to sign up.

So the battle for their hearts is unfolding this fall on campuses such as Miami's. Conservative groups including Generation Opportunity — which counts the Koch brothers among its major donors — are trying to push young people away from the exchanges and toward shopping for private-market plans at websites like Esurance, which over time could cause the collapse of Obamacare by driving up its prices.

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Groups aligned with Obama, such as Enroll America and the Young Invincibles, have marshaled their own teams to find and help sign up young people for plans through the insurance exchanges.

Generation Opportunity President Evan Feinberg said his group's sales pitch had benefited from the rocky rollout of the federal website healthcare.gov, which serves as the portal to buy insurance in 36 states, as well as from well-publicized cancellation notices from insurance companies.

"What the early numbers are showing is that this is getting to be a worse and worse deal for young Americans," Feinberg said during an interview at his Arlington, Va., office, where the sound of a ping-pong game was the first to greet a recent visitor.

White House allies are quick to counter with studies such as a late October Department of Health and Human Services analysis of data in 34 states, which showed that nearly half of uninsured single young adults may be able to purchase a plan for $50 a month or less after tax credits.

There is little hard data to indicate which side is winning. When announcing the low enrollment figures last week, Kathleen Sebelius, the secretary of Health and Human Services, declined to offer any breakdown of enrollees' ages.

Only a handful of states have released such data. In Kentucky, where the state-run exchange has been operating smoothly, 41% of the first 40,572 enrollees in private plans and the Medicaid expansion were under 35. Maryland and Connecticut released early statistics showing consumers were younger than expected.

In Washington state, which has been a bright spot among the states operating their own exchanges, 23% of the 6,351 who have signed up for private plans are 18 to 34 years old; 39% were 35 to 54 years old; and 37% were in the 55-64 age bracket.

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But health and industry experts have said the numbers of enrollees are still so small, it is difficult to predict a trend. (The Obama administration hopes to enroll at least 7 million people in this first round, including 2.7 million people ages 18 to 34.)

It is also unclear how Obama's decision last week to ask insurance companies to let Americans keep their canceled plans will affect the overall pool of enrollees. Many of the Americans whose plans were canceled are young adults who had chosen less expensive coverage.

"It's too early now to know how many people are going to enroll and what the age and health of that population is going to look like," said Robert Zirkelbach, spokesman for America's Health Insurance Plans.

Obama allies have repeatedly pointed to the experience with the Massachusetts healthcare law. There, sign-ups among the young, healthy population increased dramatically toward the end of the enrollment period, which, in the case of the federal program, extends through March.

Besides procrastination, there are several reasons younger customers are harder to secure. Those under 26 can stay on their parents' policies unless their own jobs offer insurance. Surveys also show that the group is confused about its options, highly price conscious, and — most important in terms of the political fight — still unsure whether the healthcare law is good or bad for them.

Bill McInturff of Public Opinion Strategies, who conducts the NBC/Wall Street Journal poll with Hart Research Associates, said younger Americans' approval of the healthcare law sank in the midst of the disastrous October rollout. From 2009 through most of 2013, a plurality of 18- to 34-year-olds said they thought the law was a good idea. In October, for the first time, a plurality of that age group said it was a bad idea.

At the same time, Mollyann Brodie, director of public opinion and survey research for the Kaiser Family Foundation, said her research had consistently shown that many young Americans were eager for health insurance and struggling to pay medical bills — making the term often used to describe them, "young invincibles," a misnomer.

Brodie said many young adults remained "very confused." In a recent survey, she said, the "vast majority" of young uninsured adults in California said they didn't think they would be eligible for subsidies, even though their income suggested they would.

"Most of them who probably will be [eligible] don't know it," Brodie said. "There is a real disconnect out there about the financial help that's available."

Groups on both sides are trying to fill the information vacuum.

Well-financed groups aligned with Obama like Enroll America and Organizing for America are arming their supporters — particularly mothers — with talking points to help persuade young adults to get on the government website and shop for options over the Thanksgiving holiday.

On the other side, Generation Opportunity, working with partner groups such as College Republicans and Young Americans for Liberty, is planning more stops on its college tour and its efforts to shadow pro-Obamacare groups at every turn.

Generation Opportunity is offering its allies "opt out kits" — boxes filled with banners, cozies and literature — that it mails out from its Virginia office, which has the feel of a slick high-tech firm with a floor-to-ceiling white board, for scribbling ideas, on one wall in almost every room. (The group also has a viral Web ad series, featuring an Uncle Sam figure who menaces patients, which has drawn 4 million views.)

At its events, Generation Opportunity has used iPads to sign up young people for an "opt out" pledge, thus amassing a list of names and email addresses to be used later. Feinberg acknowledges that his side's digital campaign lagged last year, but he said it had learned from the experience.

Obama's backers have "only scratched the surface of what the digital world can offer," he said. "It not only won't take long at all to start competing with what they've done, but there's a lot of room to leapfrog" past them, he said.

maeve.reston@latimes.com