Arachibutyrophobia -- do you want to find out if it really means fear of peanut butter sticking to the roof of the mouth? Do you need to know what to call your fear of computers (cyberphobia) or wonder what is the longest word in the English language (floccinaucinihilipilification)? Maybe you're curious about whether whales get venereal diseases or how long it takes a body to decompose in a pine box.

These have been a few of the hundreds of challenging questions posed every day by callers to the special telephone reference numbers of Washington area public libraries. The units, set up for ready reference and staffed by librarians, are a godsend to busy people.

As valuable as this service is, most people are totally unaware of it and the other special services and materials offered by the public library systems in Washington and surrounding suburbs. Though they "are among the best funded and most heavily used in the country," according to Arlington County libraries director Charles Brown, even many highly educated people are not library users. And even many regular users have no inkling of the broad scope of information and activities their public libraries encompass.

In affluent Montgomery County, where more than 55 percent of the population hold library cards, an about-to-be-released survey shows that 15 percent of a representative sample questioned said they did not go to the library for information on specific subjects because they never thought of it, 17 percent said they thought of it but went somewhere else, 34 percent said they thought the library would not have the information and 1 percent said they consider the library a poor source of information. Yet 78.5 percent rated the library good to very good, and 62 percent said they are willing to see more money spent on libraries.

"The assumption by most public library personnel is that they are needed and wanted," says Hardy Franklin, director of the D.C. public library system. That assumption was tested in the fall of 1980, he recalls, "when our library budget was cut, and people from every zip code wrote letters and telephoned the mayor. Newspapers also came out for the library."

Despite this proof of public support, Hardy says, "We're one of the few agencies of government begging folks to use us. We have a lot to offer, but not everyone knows it." Libraries are still battling the entrenched stereotype that they are mostly for children with homework assignments or for housewives with time on their hands or for leisure reading, not information.

Public libraries have come a long way since the first one in the United States opened in Boston in the 17th century. Everyone knows that libraries house books, newspapers and magazines, but they do not necessarily know about the 16mm films and videotapes, the records, audiotapes and compact discs of music and books, the phonograph and video cassette player equipment, typewriters and personal computers, foreign language books and pamphlets. Nor are they aware of the varied services that facilitate information gathering and programs that cater to diverse interests. Not every library system offers every service, and branch libraries within systems may offer different services, so it is useful to call ahead before traveling to the library for something particular.

Gone are the days when doing research meant laborious poring over bibliographies with minute print. Now, on-line computer searches are available to patrons at many area libraries. Businesses or individuals can request a free, up-to-date computer printout of references for any subject covered in the data base the library uses. If additional information -- such as an annotated book list -- is desired, the libraries charge for the computer time but not for the librarian's time. On-line catalogues, which more and more libraries now have, keep track of the whereabouts of materials. Reciprocal borrowing privileges among all area library systems and inter-library loan programs with libraries all over the country simplify obtaining materials identified.

The public library systems make a point, too, of developing their special collections devoted to local history with documents such as census reports, diaries, genealogy records, oral history interviews, maps, photographs and more.

The Alexandria library's manuscript and archival collection is kept at the 18th-century Lloyd House. According to director Jeanne Pitt, it is a "working library museum" and a fitting historic structure for an institution that traces its origins to a 1794 subscription library, one of the very oldest in the country.

The Arlington County Virginiana collection contains community history records. Montgomery County has a Maryland History Room in its Rockville branch, and Prince George's County has one in its Hyattsville branch. At the Oxon Hill branch, built on the site of the old Sojourner Truth elementary school, the Sojourner Truth collection houses slave narratives, rare books and other information on Afro-American history and culture. The Tugwell Room at the Greenbelt branch, where the city of Greenbelt is celebrating its 50th anniversary as a "new town," has a collection on the cooperative movement in the United States.

The Martin Luther King Library, the main branch of the D.C. library system, also has a black studies division, and Washington-history buffs can turn to the Washingtoniana Room. Since the 1930s it has maintained a newspaper clipping file, which now has 13 million clippings of anything written about the city. The Washington Post, which had acquired it, donated the clipping and photo morgue of The Washington Star to this collection. There are also neighborhood newspapers, over a million historical photographs, D.C. government documents and old plat maps that are in great demand these days when compiling neighborhood histories is fashionable. And so far 250 hours of oral history have been collected on tape. Though it is a reference-only collection -- the materials do not circulate -- it is open to children and is heavily used by third graders and ninth graders, whose school curriculum includes a unit on local history.

All the area libraries have various special collections developed for particular interests groups -- foreign language collections tailored to the immigrant populations in their neighborhoods, local authors collections, business information files and materials and equipment for the blind, hearing-impaired and physically handicapped.

The libraries also offer special services to meet the particular needs of various populations. They include visits to the homebound, correctional institutions, day-care centers and home day-care operators, retirement and nursing homes and schools. Bookmobiles, an early 20th century innovation that once served rural populations, now travel a set route every week. This summer the Prince George's County library is initiating Library on the Move, a book van modeled after the ice cream trucks that roam through neighborhoods, stopping wherever there are clusters of people. It might even be equipped with a bell to attract "customers," a sort of Good Book Truck.

The programs for children and adults, which all the library systems sponsor, make them focal points for their neighborhoods. Explains Agnes Griffen, director of the Montgomery County Department of Public Libraries: "Libraries are community centers as well as information centers. Our Olney branch is known informally as town hall. At Wheaton there's a newcomer's packet with information for people new to the area."

Increasingly, homeless people have been using libraries as daytime shelters. So the Montgomery County library system has developed a printed handout with information about finding food and shelter. The D.C. library has gone much further by developing its Community Information Service, a constantly updated on-line information bank of more than 900 federal, municipal and private organizations that provide such services as legal aid, day care, adoption, student exchange programs and recreational activities. Computer terminals for access to this information are located not only at the main branch but also at the University of the District of Columbia and D.C. public high schools.

In keeping with the community role of libraries, the Martin Luther King Library opened "The Other Place," its young adults room, equipped with phonograph stations and popular records, video players and tapes as well as hardbound and paperback books. It is designed to be a place where teen-agers feel comfortable spending time after school and where they can find out that libraries can be fun.

And all library branches have separate children's reading areas. Behind this emphasis on collections and programs for children is the belief that librarians can help children become lifetime readers and library users. Storytelling hours, puppet shows, crafts activities, film showings and rewards for following a set reading program are all intended to keep children interested in books. Book discussions and on-going book clubs do the same for adults.

With 1987 designated "The Year of the Reader," librarians around Washington are hoping that people will "think library first." Gail Forman is a professor at Montgomery College, Rockville.