THE SCENE AT Jefferson-Houston Elementary School in Alexandria one day last spring could not have been more perfect if a Madison Avenue ad man had staged it:

A handful of wide-eyed second graders were looking over a rainbow array of brand-new paperbcks spread out on the tables in their reading room. They'd been told not to touch the books until the rest of the class arrived, but their hands were obviously itchy. A cherub-faced little boy pointed a pudgy finger at one he liked. "Oh, wow," he whispered, "I hope I can have that one about George and Martha."

This George and Martha are a pair of smiling hippopotamuses.

Scenes like that one are played out several thousand times a year in schools and libraries across the country as part of a program called Reading Is Fundamental, and Madison Avenue -- as well as Capitol Hill -- play no small part in bringing them about.

Reading Is Fundamental Inc. -- known as RIF -- is a private, nonprofit organization, supported largely by foundation grants and private donations, that helps community groups organize book giveaways for children. RIF's philosphy is simple: Let children choose, for themeselves, books that they may keep and take home, and in due course they will probably learn, not only to read, but to like to read. Its aim is admittedly high: It would like to prevent future generations of schoolchildren from joining the estimated 23 million Americans who are functionally illiterate.

RIF was founded in 1966 in Washington by Margaret C. McNamara, who still serves as chairman of the organization. For its first two years, RIF operated as a pilot project in a handful of D.C. schools. Then, in 1968, with a $285,000 grant from the Ford Foundation, RIF tried out its program in selected communities around the country. It grew steadily, if slowly, until in 1976 a federal matching-grant program was instiuted, giving local RIF organizations $3 for every one they could raise themselves to purchase books. Then RIF really took off. It has grown from about 400 local projects in the mid-1970s to more than 4,000 today; the size of its national staff, which provides technical assistance and arranges for purchasing discounts (usually about 40 percent) with publishers, has jumped from 10 to more than 50, currently housed in crowed offices at L'Enfant Plaza. RIF has programs at about 13,000 places in all 50 states, D.C., Puerto Rico, the Virgin Islands and Guam. The vast majority of them are in schools, others are found in libraries, hospitals, schools for the blind, dentention centers, jails and bookmobiles. RIF estimates that in 1980 local groups will give an average of four books apiece to more than 3 million children ranging in age from 3 to 18 (though about two-thirds of them are in elementary grades).

RIF's success is apparently due to the right mix of organizational know-how, political clout and extemely savvy public relations. Much of the credit for putting that recipe together must go to Margaret McNamara.

As she tells it, the idea for RIF was born when, as a volunteer reading aide in the D.C. public schools, she encountered two 5th-grade boys with severe reading problems.

"One of them told me he had never had a book of his own. When I brought in some of my son's books for the boys, they were just amazed that anyone would give them a book," she recalled.

As the wife of the then secretary of defense, Mrs. McNamara was no stranger to the ways of politics. Instead of simply going home to ransack the attic for second-hand books, she organized a citywide project, and made sure it got plenty of attention. She gathered several dozen representatives of schools, libraries and civic groups around the city; she and they raised a fair sum of start-up money from a number of small foundations; and, in typical Washington fashion, they kicked off the program with a press conference -- two days after the conference, the local media were on hand to see the very first RIF book distribution.

That same instinct for turning a simple good intention into a program that reaches millions of children has informed the RIF organization from the start. In 1971, the Advertising Council approved RIF as a "public service," thus qualifying it for millions of dollars worth of free advertising. The Al Paul Lefton Agency in New York volunteers its services to put together RIF's advertising campaign, and celebrities like Carol Burnett and Ed Asner give their time, free, to make the commercials.

RIF has consistently been able to attract wellplaced persons to its cause. The federal matching-grant legislation that helped propel RIF to its present position was introduced in the House of Representatives by former Congressman Albert Quie, (R-Minn.), now the governor of Minnesota, who, in the words of one Capitol Hill staff member, "did it for Mrs. McNamara." Last October, RIF celebrated the International Year of the Child with an enormous book giveaway for Washington area schoolchildren -- hosted by Amy Carter at the White House.

Since merely dropping a single book into the hands of a child will not convince him that reading is either fun or fundamental, RIF requires its local groups to hold at least three book distributions in a school year -- five in a calendar year -- and encourages the groups to continue the project for more than just one year. Local volunteers must also devise a variety of "motivational activities" both leading up to and following every distribution. And to insure that the choice of books fits the mix of children to receive them, the books must be selected by a local committee that is representative of the community, usually teachers, librarians and parents.

Despite the apparent success and the almost missionary zeal of RIF, there is no objective, conclusive way to judge whether or not the idea really works. There are, of course, numberous testimonials from school principals, librarians, and like. Surveys of parents and teachers tend to show that RIF does make inroads among previously unmotivated readers. Still, says Ruth Graves, president of RIF, the effectiveness of the program is "very difficult to measure." The organization is forced to rely on impressions and imperfect yardsticks that only "tend to lend credibility" to RIF philosophy, she says.

The one area of the RIF program that has met with a good deal of resistance, if not outright criticism, is the selection of books that are offered to the children. RIF insists that children in their programs be allowed to choose for themselves the books they would like to have -- a condition that many adults seem uneasy with. The books given out at RIF distributions range (depending on the ages of the kids involved) from established "classics" like Charlotte's Web by E. B. White or A Separate Peace by John Knowles to titles like Darth Vader's Activity Book, and Strange But True Football Stories.

Teachers especially, but many parents as well, seem to want to steer their charges toward the books with more apparent "literary" value. One young mother who works as a volunteer for the Northern Virginia RIF organization, which oversees individual projects like the one at Jefferson-Houston, admitted that when she sees her own kids reading something like Jimmy Walker: The Dyn-O-Mite Kid, she has to stifle the urge to discourage such stuff.

"You've got to get them reading something," she insisted, "before they'll start reading the classics."

There are experts in the field who agree. "You learn to read by reading," says Robert Wilson, director of the reading center at the University of Maryland's College Park campus. "If we were all to look back on our own lives," he says, "we would realize that an interest in serious literature came at a different time for each of us."

The best argument for RIF probably comes from the kids themselves. One second grader at Jefferson-Houston, for example, solemnly explained that his mother and father never read to him because they're too busy, but that he really likes to read to himself. He proceeded to tick off the title of every book he'd ever received through RIF.

Sometimes the program even works a little too well. One of the RIF organizers at Jefferson-Houston, trying to pique her students' interest in the books that were about to be given away, described each of the titles in turn. She held up one called A Crocodile's Tale, in which a hungry beast tries to devour a little boy: "Do you think the boy can escape from the jaws of the crocodile?" she asked mysteriously.

"He can," a small voice announced, with the merest hint of boredom. "I already have that one."