THERE ARE between 17 million and 18 million books in the library of Congress - no one knows the exact number - and a third of them are rapidly turning to dust.

Frazier Poole, head of the library's preservation and restoration unit, set behind his desk in the Thomas Jefferson annex recently, crumbling bits of dry paper between his tumb and forefinger. "There are an estimated 5 to 6 million volumes that cannot go to a binder because the paper is so brittle," he said. "People can't use them.

Books from the United States or abroad, are printed on paper which deteriorates in this manner in 50 to 75 years, Poole said.

The library abounds in situations like this, not the least of which is that only about $20 million of its $141-million annual budget is allocated for direct support to the Congress, a primary purpose to which all, including Librarian of Congress Daniel J. Boorstin, pay lip service.

The libray preserves such varied hallmarks of Western culture as comic books, selected pornographic novels and Stradivarius violins.

It accquires "one and a half items every second of the working year," according to Boorstin. Part of the library is in an old weapons building at the Navy Forces Base in Ohio.

The Library maintained relations with the Egyptian government after the 1967 Middle East war when the United States government did not.

Boorstin and other officials note that the Library of Congress is a national institution like the British Museum in the United Kingdom and the Bibliotheque Nationale in France. It has a mandate to document the flow of American civilization; yet two-thirds of its books are in languages other than English.

The Library of Congress is dedicated to the free dissemination of knowledge - boorstin asserted that it is far more accessible to the general public than in European national libraries - but it engages in secret classified research for the Defense Intelligence Agency.

When asked why the library does it, the Pulitzer prize-winning historian who became librarian in November, 1975, said:"

I have no answer for the Defense Intelligence Agency question." Boorstin said that Congress, not he, determines whether or not the library should engage in classified research, for the Pentagon or anyone else.

The library's budget is almost 15 per cent of the billion dollars that Congress appropriates annually to pay for its own operations. There are those in Congress who find this highly inappropriate, expecially because most of the benefit of the public and not the legislators.

What began in 1800 with a $5,000 purchase of 740 volumes has grown today to a collection of perhaps 74 million items whose total value is inestimable.

The library's collections of uncunabula (books printed before 1500), films and photograph records are among the world's greatest. Its millions of books are honeycombed throughout several buildings on 336 miles of shelves.

But they are also piled on floors, crowded into corners and generally in disarray. There are many thousands of items that are believed to be in the library, but can't be found.

The library produces and sells catalog cards - millions of catalog cards at 15 cents a piece - to other libraries here and abroad. It is trying to phase itself out of the card business as quickly as possible and put everything in machine-readable form but the process is relatively snail-like. The library's main catalog contains more than 23 million cards in about 30,000 file drawers.

Exact numbers are hard to come by in the library, which is easy to understand given the enormous volume of material in its collections.

John Broderick, chief of the manuscript division, says, for example, that "no one has near the number of documents we have in a non-archival setting - it's around 35 million." An annual inventory of 35 million items - more or less - is simply no practical.

It's not just the amount of material that is mind-boggling. The most stunning figures relate to the volume handled by individuals. The three-member selection staff, for example, must consider upwards of half million books a year, deciding in spilt seconds, usually just on the basis of a publisher's imprint, which works to keep and which to toss on the scrap heap of history.

The music division has done away with that problem. According to Barbara Henry, assistant chief of the department's reference section, "I don't think the music division has ever thrown anything away."

Every rock or pop song that comes into the library, usually through copyright deposit, finds a home in the music division. That comes in handy, Henry said, because congressmen often ask for the lyrics to pop songs, presumably to quote in speeches. "One man's Garbage"

BARBARA RINGER, who heads the library's copyright division in Crystal City enthusiastically described another of the library's pop culture collections - comic books - most of which were also acquired through the copyright law, under which two copies of all pieces of published material are deposited to register the copyright.

"The comic books are not organized, but they are all here in this [main library] building," she said. "They are more important than some of the scholarly writing. One man's garbage is another man's social history."

Begining in 1978, the Library of Congress will issue licenses for juke boxes and allocate payments to song writers based on the number of plays their records get.

A new copyright law, which provides for the juke box licensing, also mandates the library to set up a television archieves and to monitor some 4,000 cable television outlets, performances on which will be subject to the law.

Perhaps the library's wildest anomaly is in the rare book division, which is headed by William Natheson, a soft-spoken, elegant man who works in an odd little cubicle - the library has dozens if not hundreds - which appears to be twice as high as it is either long or wide.

"We're bringing into the division pulp fiction and weired tales," Matheson said, "which are now seen as solid research material. We're not out to buy books because they're rare, but because we need them."

What the rare book division can buy is severely limited. The budget for the division's acquisitions is only about $6,000 to $7,000 a year. At a recent book auction, a copy of William Carlos Williams' first volume, "Poems," brought $16,000. Ezra Pond's privately printed "A Lume Spento" went for $18,000.

Matheson pointed out that his division has patrons and gifts are not uncommon, but he added a bit wisfully, "I do think we've had a pittance with which to work." Only 1 per cent of the library's total budget goes for book purchases.

Lest all this seem a mad mixture of frivolity, 21st Century technology and 12th Century working conditions, it should be known that that is only a part of the story - possibly the most entertaining part, but not the most important.

The library is an outstanding center of scholarship.

Some of its collections are among the finest in the world. And there is no questioning the seriousness of Boorstin and his professional staff.

Alan M. Fern, a former professor of sociology at the University of Chicago who heads the library's research department, says the library professional staff is every bit the equal of a good university faculty. Boorstin agrees.

Fern cited Broderick, an authority on 19th Century American literature; Jerald Maddox, whose field is art history and the history of photography, economist Harry Gourevitch and musicologist John Newsom as among the many library scholars who would grace any university campus.

By its sheer physical presence, the library seems to command the right to a role of leadership in American cultural life.

"Sculpture and paintings, rare marbles, and a broad scheme of color and of ornamentation in stucco relief unite with a lofty architectural design to form what is one of the most notable interiors in the country," is the way a library handbook describes the main reading room.

Fern summed it up when he said, "When you read a book in there, you're really reading."

The problem is that to get your book it takes 45 minutes to an hour and a half, if you get it at all. The main reading room has only about half as many employees per book working in the sacks as the New York Public Library and about 20 per cent of the collection is missing from the shelves at all times.

"We're just about up against the wall in terms of volume," said Fred Croxton, who is in charge of reader services. "On a recent Saturday afternoon, there were 3,400 requests for books and only 25 to 27 people working in the stacks."

Croxton said that in the past the library had been "too conservative" in its estimates of how many staff members were needed to service the reading rooms, but that 14 more were being sought in the 1978 budget request.

Croxton also said that previous requests to Congress for more help have not been fulfilled. Services for Congress

IN ANOTHER division of the library, regular staff increases have been provided for by law. That division is the Congressional Research Service (CRS), which gives direct support to the members of the Senate and House, their staffs and committees.

Dozens of services are provided to congressmen by the CRS, which former acting director Norman beckman calls "the biggest and probably the best think tank in town."

CRS researchers will spend months preparing a study of the economic and social costs of unemployment or minutes turning up a statistic such as how many food-stamp recipients are on welfare.

They will do extensive digging into the background of a prospective presidential appointee so that congressional committee members are armed with an arsenal of questions.

CRS staffers prepare digests of bills, 8-to 15-page summaries of major issues confronting Congress - ranging from mechanically deboned meat to cruise missiles - and extensive bibliographies, any of which a senator can view instantly on a television screen in his office, which is plugged into the service's computer.

Ninety-three Senate offices and 24 Senate committees have video display terminals, for which they pay about $100 a month, and machines that will provide a printout should the senator or his staff require it. About 100 House members have terminals and most members are expected to have similar systems by the end of this year.

CRS staffers do translations from 22 languagues and prepare maps and charts. They write speeches for members of Congress, draft floor statements used to introduce bills, consult on a regular basis with committee staff members on their specialities, help draft committee reports, write letters on technical matters for congressmen and organize seminars.

Congress makes use of CRS services on a massive scale. Last year the researchers and librarians answered 291,000 requests from members and staff and this year the total is expected to be well over 300,000.

CRS is second only to the division of the blind and physically handicapped in the size of its budget, which totaled $20,261,000 in the fiscal year 1977. The budget for producing and supplying talking books is $21,818,000.

The division of the blind and physically handicapped serves half a million persons in the country and has about 11,000 titles available for distribution on discs and tapes. The usual number of copies produced is 1,000, but for "Roots," for example, it was 5,000.

The recordings are done at very slow speeds so that a book will not take up numerous discs or tapes, but the machines the blind persons use, which are supplied by the library, are equipped with controls allowing the tapes and records to be played at faster speeds so that it doesn't take forever to finish a book.

The library also has a serials division, which among other things has the largest collection of newspapers in the world. It receives on a daily basis 973 foreign newspaper and 306 domestic dailies. All told, there are 125,000 poriodicals - that figure represents titles, not individual editions - in a collection that ranges from dime novels (about 15,000) to the New England Journal of Medicine.

The serial division is now setting up the first inventory of at least one edition of every daily newspaper ever published in the United States.

The library's loan division processes about a quarter of a million transactions a year, mainly loans to other libraries across the country.

The music division, aside from making available to the public its collection of 4.5 million items, including 675,000 phonograph records, stages concerts and makes recordings. New Techniques Sought

A GREAT MANY of the library's approximately 5,000 employees do tedious rote jobs, which range from putting cards in alphabetical order through assigning Dewey decimal numbers to cards for books that have already been cataloged in two other ways to preservation and restoration of books.

According to William Welsh, deputy director of the library, "Material coming in today from India is in worse shape than the Gutenberg Bible."

The reason, Poole explained, "is that around the time of the Civil War rags became scare and papermakers wanted to make more at less cost, so they turned to wood pulp, which is not strong. They also switched from gelatin sizing to alum resin, which creates acid in paper in the presence of moisture in the air."

Not only is the paper poor, but the books are badly bound. "Publishers' bindings are notoriously weak," Poole said.

Poole and others at the library agreed that it was hopeless to expect publishers to raise their costs by switching to better quality paper or doing a better binding job, so they are looking for other solutions to one of the library's most pressing problems.

The emphasis is on developing new preservation and restoration techniques for those materials that are best kept in book form, and microfilming the rest.

Half a million dollars a year is currently being spent on microfilming at a cost of about $25 per 300-page book.

Restorations are much more expensive. Some restorations can most hundreds of dollars per book, or in especially difficult cases hundreds of dollars per manuscript page, Poole said. The destructive acid is removed from the paper by bathing each page individually in an aqueous or solvent solution, which causes tha pages to swell, making rebinding necessary.

The library's lab is constantly looking for new, better and cheaper ways to preserve books. Efforts are focusing on a way to deacidify the paper by blowing a solution into the press without taking the book apart.

Specialists are also aging books 500 years in 48 days in special ovens to help them discover ways to slow the aging process on the shelves. And other experts are engaging in the most painstaking kind of work to restore books and other works on paper in the library collection.

One woman has been restoring a tissue-thin Japanese watercolor for two years. There is a man who does nothing but oil leather bindings.

The Library has also been in the forefront of technological advancement in numerous areas other than restoration of books in recent decades. The 33 rpm record was born in a library laboratory; a new machine is being designed for the library by the Xerox Electro-Optical Systems Division which will set type not only in Roman characters, but in Hebrew, Arabic, Chinese and Japanese.

Yet, in this temple of enlightened research and scholarship, hundreds of people are doing the most deadly kind of rote work in an oppressive Dickensian atmosphere.

A congressional staffer who is knowledgeable about the library said that "the biggest is supervision of employees to get more productivity," but he acknowledged that the nature of much of the work did not lend itself to enthusiastic performance.

When Jean Metz, head of the book selection staff, and one of her assistants, Lolita Silva, were asked what their job satisfactions were, Metz answered by asking Silva rhetorically. "Do you have any?"

Bede Sullivan, a Columbia University English graduate, catalogs books in more than 50 African languages, although he knows only Swahili well enough to really read it.

He acknowledges that the work is tedious. There are, he says, interesting aspects to the jobs, which involves extracting from the book the kind of information you find on an ordinary library catalog card, but he can't find the words to express what those aspects are.

The congressional library watcher, who did not wish to be identified by name, characterized working conditions throughout the library's many buildings as "horrible." He is not far off the mark.

Sullivan works in a large room at a tiny book-cluttered desk, smack up against another tiny book-cluttered d+sk, and so on down the line, in row upon row of small, cluttered desks.

Out at the Navy Yard, one group of employees of the division that sells catalog cards to other libraries spends the day selecting catalog cards in an enormous room lined with dingy gray file cabinets. Their boss, David G. Remington, chief of the catalog distribution service, said: "You can see how hard it is to pull out those card drawers all day and still remain human."

Elsewhere, people work at tiny cramped desks in tiled corridors. There are rabbit warrens of glass and gray green wallboard partitions with aisles barely wide enough for one person. Yet all of this has been installed under the richly painted ceilings, the deteriorating ornamental plaster work, of an extraordinary building. It resembles a 19-Century London slum relocated inside a Renaissance palace.

Boorstin intends to begin returning it so its original condition just as soon as the library's third major structure on Capitol Hill, the $123-million James Madison Building, is ready for occupancy.

The move into the 15-million-square-foot building, which reminds some critics of the monumental architecture of the Third Reich, is scheduled to begin in early 1979 and it is estimated that it will take a full year to complete.

The new building will not accomodate the hundreds of people who work out at the Navy Yard and it provides no room for growth. It will take in the employees who work in the map division in Alexandria and the division of the blind and physically handicapped on Taylor Street NW.

The collection of early nitrate films will remain in special cold-storage vaults at Wright-Patterson Air Force Base. The Madison Building will not have cold-storage facilities.

Despite the problems, Boorstin is optimistic and enthusiastic about the library's future.

"We have an opportunity to make this place into a wellspring rather than a warehouse," Boorstin said. "The terms sound rather grandiose, but this is a grand institution. In the age of television, the Library of Congress is an island of choice in a world of Channels."