Almost unnoticed among the iron-grilled storefronts and derelict tenements off the busy Harlem intersection of 135th Street and Lenox Avenue, the Schomburg Center for Research in Black Culture appears closed, even when it's open.

Inside, the three-storey building that was designed in 1905 by famed architect Stanford White has the expected opaque tarnish of a library. Yet, to the dismay of itsnotable constituents, and despite the fact that it is one of the world's richest black history repositories, the Schomburg has more than its share of dowager shabbiness and financial troubles.

The paint has peeled in many places; a rope and container hang over the stairway to transport books. Water marks from leaks have stained the walls. There is neither elevator nor air-conditioning. Erratic heating forces the library to close when the temperature inside drops below 68 degrees.

The chronic financial difficulties of the 51-year-old institution, intensified by New York City's fiscal crisis, have prompted a national fund-raising drive primarily to match a $150,000 preservation grant from the National Endowment for the Humanities.

Headed by Ruth Bunche, widow of the Nobel Peace Prize-winning scholar and diplomat, historian John Hope Franklin and Robert C. Weaver, former Under Secretary of the Department of Housing and Urban Development of list of committee members includes both Rosalynn Carter and Betty Ford. Money for a long-planned new structure recently was approved.

Although in recent years the Schomburg has suffered at the hands of near bankruptcy - "It's very sad indeed," comments Franklin - in the past, work pursued at the Schomburg helped change the course of history.

Generations of scholars on the Afro-American experience have relied heavily on its books and manuscripts. Even when Howard University's Alain Locke, notable cultural theoretician and author of the milestone 1925 volume, "The New Negro," was too sick to maneuver the stairs, he continued to use the library by staying on the first floor. Psychiatrist Kenneth B. Clark's research on segregation, done mainly at the library, was cited in the 1954 U.S. Supreme Court school desegregation decision. Brown vs. Board of Education.

Over the years, some of the most valuable materials on the black experience have been deposited there including the 81-manuscript volumes of field notes and memoranda used by Swedish social scientist Gunnar Myrdal for his landmark study, "An American Dilemma."

Beyond its research role, the Schomburg has functioned as an art gallery with both cmtemporary and rare African works, as a lecture hall and as a home for ground-breaking black theater companies. One production that started in the library's basement, "Anna Lucasta," went to Broadway, and many black actors, such as harry Belafonte and Robert Earl Jones, father of James Earl Jones, did early and important work there.

So closely identified with black cultural traditions is the Schomburg that a musical scene on the library appears in th current Broadway hit revue "Bubbling Brown Sugar." A man in the street asks, "Where you taking that trunk?" Another character, holding a hat symbolic of comedian Bert Williams' actual gift of some personal belongings to the library, replies, "To the Schomburg where the history of Harlem is kept."

It was in the dusty, isolated stacks that August Meier found many of the documents that helped forge his "Negro Thought in America 1880-1915" into a distinguished text. Using the correspondence between Booke T. Washington, the late 19th-century black educator spokesman, and Francis J. Garrison, a newspaper writer whose letters are deposited at the Schomburg, Meier showed that Washington had worked vigorously and secretly to tone down his image as an accomodationist. In one letter, Washington said he didn't want to appear with a black supporter of segregation because the man "had the reputation of simply toadying to the Southern white people."

Meier, like many other historians, has by no means depended exclusively on the Schomburg. The other major collections of black materials are divisions of universities: Howard, Harvard, Yale, Fisk, Dillard, Atlanta and Hampton. Ironically, part of the Schomburg's budgetary and structural problems have resulted from its association with public financing instead of academic endowments.

Even its curators have become well known and influential cultural personalities. Arthur Schomburg, the curator from 1932 to his death in 1938, was a Puerto Rican of African descent.He built an extensive private library from the money he earned as a bank clerk and donated his collection to the city in 1925, helping to create the Division of Negro Literature, History and Prints, later renamed in his honor. He was succeeded by Lawrence Reddick, a historian and the first biographer of the Rev. Martin Luther King Jr., and by Jean Blackwell Hutson, curator for the last 28 years.

"We have never had a slack period for requests," said Hutson, an effervescent woman who has shepherded the library through many different phases of interest. Seated in her tiny and crowded office, Hutson recalled the research of authors Ralph Ellison and James Baldwin, artist Romare Bearden, of students such as Kwame Nkrumah who later became the leader of Ghana. She remembered the demands placed on the library by the interest in African history during the Independence Movements of the '50s.And she talked of today and of the almost overwhelming demand for black materials during the '60s.

Hutson's own introduction to literature and its personalities began during her Baltimore childhood when such writers as Countee Cullen and Langston Hughes would stay in neighbors' boarding houses. Later, through the libraries and her first marriage to Andy Razaf, a songwriter and poet, she continued her contact with th social, political and cultural luminaries.

Hutson unlocks the door of a rare book case and selects one of the collection's true treasures, a faded green book "Ad Catholicum" by Juan Latino, the oldest book known to be written by a black, published in Latin inn 1573.

Also included in the Schomburg's rate holdings are the military orders of Toussaint l'Ouverture, the leader of the Haitian Revolution, the first edition of domestic worker and former slave Phillis Wheatley's "Poems on Various Subjects" (1773) and the original almanacs of Benjamin Banneker, the mathematician who helped Pierre l'Enfant on his original plan for the city of Washington. Today's Schomburg holdings include 100,000 books, 250,000 manuscripts, 5,000 art objects a 100,000-item vertical fiel (being converted to microfilm by a 14-member staff from the Endowment), all the black newspapers published since 1827 and an 3,500 phonograph record collection. More than 50 per cent of the material deals with Africa.

Much of Hutson's energies are spent battling for the Schomburg's future. Part of her anxiety was eased recently with the approval of a $3.7 million grant from the Federal Works project Bill for the construction of a new building adjoining the present site.

In the mid '60s, she recalled, "We were simultaneously feeling the pressure of the black studies boom and the ranting of wierd characters who said integration would absorb all black culture into the mainstream. But people want the Schomburg. It's too vital to ever lose its preeminence."