President and Mrs. Reagan will stick around the White House for Christmas, then fly to California the day after for a holiday reunion with old friends. Among the festivities planned is the annual New Year's Eve house party at the Palm Springs estate of Walter and Leonore Annenberg. That trip will bring to 15 the number of private outings the president has made since taking office 23 months ago.

The media explosion on the brain -- through newspaper series, magazine cover stories and television specials -- only confirms that the public is finding out what researchers have long known: The brain is one of medical science's hottest new research areas. Later this week at the National Institutes of Health, a dozen or so experts will get together to brainstorm, courtesy of an Academy Award-winning actress.

Jennifer Jones, who once attempted suicide and whose family problems have included dealing with the suicide of her only daughter, set up a foundation in 1979 along with her billionaire husband, Norton Simon, to encourage research into the causes of mental and emotional disorders. The Jennifer Jones Simon Foundation has sponsored four scientific get-togethers on a variety of related topics since then. This year's -- being held in Washington for the first time -- will focus on "Mind and Body."

Among the scheduled discussions: A Swedish scientist's findings that there are biochemical differences between "successful" suicides (those who die) and those who "fail" (those who live); an English psychologist's investigations on the "sight" that blind people develop through an acute sense of objects around them; and an American researcher's explorations of brain functions by studying bird brains, whose "song centers" shrink when seasonal changes halt singing.

Unlike most scientific meetings, the emphasis is on informality. "We tell scientists to 'Come and bring your thinking--not your papers,' " says Dr. Herbert Pardes, director of the National Institute of Mental Health, who will chair the workshop.

For Jennifer Jones, who has pounded a few congressional corridors in recent years seeking support for mental health research and funding, the workshop's Washington setting provides one decided advantage.

"Many of the influential allies who neuroscientists need are here," she says. "The hope is to increase public awareness of this exciting area of brain research because it has such a personal impact on the mental health of people everywhere."

To help implement that, she and Simon are giving a couple of dinner parties for their scientific conferees. One will be at the Four Seasons Hotel where the bipartisan guest list is expected to include senators Mark Hatfield of Oregon, William Proxmire of Wisconsin, Ernest Hollings of South Carolina and Ted Stevens of Alaska.

Barbara Bush spotted the similarities the other day in Zimbabwe when she presented an award to an American woman who founded The Adult Literacy Organization (ALO). Alice Sanderson, like the late Margaret McNamara of Washington, had worked for many years to stamp out illiteracy. Also, like McNamara, Sanderson's idea to improve the quality of life became something lasting. In its 20 years of existence, ALO has opened tutoring centers throughout Zimbabwe, which have become models for programs being set up by the government.

Margaret McNamara's "modest experiment," as she often called Reading Is Fundamental (RIF), also has grown in the 16 years since she founded it. Today, RIF has channeled more than 50 million paperbacks into American homes by motivating youngsters to read through letting them choose -- and keep -- the books. And from a single project in Washington, D.C., RIF has multiplied to 3,000 in all 50 states. Maggie McNamara died in 1981 shortly after President Carter recognized her efforts by awarding her the Presidential Medal of Freedom. Tomorrow night at a ceremony in the National Portrait Gallery, RIF will immortalize her by presenting its first annual Margaret McNamara Memorial Award.

That's the presentation RIF board member Barbara Bush will make to a 79-year-old judge whose own life has been devoted to improving the quality of life for young people. She is Judge Mary Conway Kohler, herself founder of the National Commission on Resources for Youth and developer of a plan for administering New York City's Family Court. In the invitation-only audience will be former defense secretary and former president of the World Bank Robert McNamara, who was Maggie McNamara's husband.