The Obama administration is planning a decade-long scientific effort to examine the workings of the human brain and build a comprehensive map of its activity, seeking to do for the brain what the Human Genome Project did for genetics. The project will include federal agencies, foundations, and teams of neuroscientists and nanoscientists in a concerted effort to advance the knowledge of the brain’s billions of neurons and gain greater insights into perception, actions and, ultimately, consciousness. Scientists also see it as a way to develop technology to understand diseases like Alzheimer’s and Parkinson’s and find therapies for a variety of mental illnesses. Moreover, the project holds potential to pave the way for advances in artificial intelligence. The project, which could cost billions of dollars, is expected to be part of the president’s budget proposal next month. Four scientists and representatives of research institutions said they participated in planning for what is called the Brain Activity Map project. The details are not final, and it is not clear how much federal money would be proposed. In his State of the Union address, President Obama cited brain research as an example of how the government should ‘‘invest in the best ideas.’’ Story C. Landis, director of the National Institute of Neurological Disorders and Stroke, said that when she heard Obama’s speech, she thought he was referring to an existing project to map the static human brain. ‘‘But he wasn’t,’’ she said. ‘‘He was referring to a new project to map the active human brain.” Francis S. Collins, director of the National Institutes of Health, may have inadvertently confirmed the plan when he wrote in a Twitter message: ‘‘Obama mentions the #NIH Brain Activity Map in #SOTU.’’ A spokesman for the White House declined to comment. The initiative, if successful, could help lift the economy. ‘‘The Human Genome Project was on the order of about $300 million a year for a decade,’’ said George M. Church, a Harvard University molecular biologist who helped create that project and said he was helping to plan the Brain Activity Map project. ‘‘If you look at the total spending in neuroscience and nanoscience that might be relative to this today, we are already spending more than that. We probably won’t spend less money, but we will probably get a lot more bang for the buck.’’ Scientists involved in the planning said they hoped that federal financing would be more than $300 million a year. The Human Genome Project cost $3.8 billion. It was begun in 1990 and its goal, the mapping of all the genes in human DNA, was achieved ahead of schedule, in April 2003. A federal study of the impact of the project indicated that it returned $800 billion by 2010. The advent of technology that allows scientists to identify firing neurons in the brain has led to numerous research projects. Yet the brain remains one of the greatest scientific mysteries. But nanotechnologists and neuroscientists say they believe that technologies are at hand to make it possible to gain a more complete understanding of the brain, and less intrusively. In June in the journal Neuron, six scientists proposed new approaches for mapping the brain. One possibility is to build a complete model map of brain activity by creating fleets of molecule-size machines to noninvasively act as sensors to measure and store brain activity. However, some scientists say understanding the human brain presents a drastically more significant challenge than mapping the genome.