Look for a fundamental shift in how scientists hunt ways to ward off the devastation of Alzheimer’s disease - by testing possible therapies in people who don’t yet show many symptoms, before too much of the brain is destroyed.

The most ambitious attempt: An international study announced Tuesday will track whether an experimental drug can stall the disease in people who appear healthy but are genetically destined to get a type of Alzheimer’s that runs in the family. If so, it would be exciting evidence that maybe regular Alzheimer’s is preventable too.

A second study will test whether a nasal spray that sends insulin to the brain helps people with very early memory problems, based on separate research linking diabetes to an increased risk of Alzheimer’s.

The new focus emerges as the Obama administration adopts the first national strategy to fight the worsening Alzheimer’s epidemic - a plan that sets the clock ticking toward finally having effective treatments by 2025.

“We are at an exceptional moment,” with more important discoveries about Alzheimer’s in the last few months than in recent years, Dr. Francis Collins, director of the National Institutes of Health, declared Tuesday.

But a meeting of the world’s top Alzheimer’s scientists this week made clear that meeting the 2025 deadline will require developing a mix of treatments to attack the different ways that Alzheimer’s damages the brain - much like it can take a cocktail of drugs to treat high blood pressure or the AIDS virus.

Perhaps more importantly, it will require testing possible drugs before full-blown Alzheimer’s sets in, when it may be too late to do much good. After all, Alzheimer’s starts ravaging the brain at least a decade before memory problems appear. And doctors don’t wait until the worst symptoms appear before treating heart disease, cancer or diabetes, noted Dr. Reisa Sperling of Harvard Medical School.

“Once the train leaves the station of degeneration, it might be too late to stop it,” Sperling said. “We need to define the critical window for intervention.”

Future therapy is far from the only goal of the first National Alzheimer’s Plan. It’s a two-pronged approach, promising to provide better and support for overwhelmed families along the way.

“A lot more needs to be done and it needs to be done right now, because people with Alzheimer’s disease and their loved ones and caregivers need help right now,” Health and Human Services Secretary Kathleen Sebelius said in announcing the plan.

Among the first steps: A new website - http://www.alzheimers.gov - that Sebelius called a one-stop shop for families offers easy-to-understand information about dementia and links to resources in their own communities. The government will offer free training to doctors and other health providers on how to spot the early signs of Alzheimer’s and care for those patients. This summer, a campaign will begin to improve public awareness of Alzheimer’s, important in reducing the stigma that helps fuel late diagnosis and the isolation that so many affected families feel.