In a moment of inspiration, artist Don Miller seized on the idea that when Martin Luther King Jr.'s birthday becomes a national holiday in 1986, a massive mural depicting the slain civil rights leader's life should be unveiled in the main Washington library that bears his name.

D.C. public library officials obliged him; Miller was given a contract in November to research, design and paint the $250,000 oil-on-canvas work that will tell the story of King and the civil rights movement in 83 scenes and faces. The mural is scheduled to be unveiled publicly a year from today

"I always wanted to do something important with my art work," said Miller, 61, a Montclair, N.J., illustrator and portrait artist. "I wanted to do something that would have everlasting value."

Coordinators of the project said they received significant public response and contributions after D.C. Mayor Marion Barry announced the mural plan at a celebraton of King's birthday last Tuesday.

"To date we've raised $40,000 in cash contributions," said mural coordinator Barbara C. Washington. "I think that this can be regarded as an indication of the support for the project, but more importantly, it indicates the universal appeal that the project will have in the community as well as the country."

A working rendition of Miller's mural begins with scenes from King's early years, including his days at Morehouse College in Atlanta, where he was influenced by school president Benjamin Mays and the writings of Mohandas Gandhi, both of whom are pictured. It ends with King's tomb.

The mural, a library consultant said, has become the focus of the library's first major fund-raising drive. Library director Hardy R. Franklin said that about $500,000 is being sought.

After the mural is purchased, the rest of the funds are to be used for library needs, including a climate-control system to retard the deterioration of books and othesr materials. Barry has pledged to include the mural project in his 1986 city budget, matching "dollar-for-dollar the citizens' contribution."

The mural will measure seven feet by 56 feet and will be mounted on the black steel girders along the north wall of the library's lobby.

Among the mural's many faces, tentatively planned likenesses include those of D.C. Del. Walter E. Fauntroy and Barry, both civil rights leaders in King's time.

In a series of overlapping images, the mural features a historic broad brush of meetings and marches, fire hoses and black youths, jail blocks and martyrs, all amid the symbols of the turbulent times that led to King's assassination in 1968.

The mural's two 28-foot panels end with King's tomb in Atlanta located in the neighborhood of his church and his birth.

"For me, I think this is very much like King," said library director Franklin, a classmate of King's at Morehouse. "He was a simple man . . . . His life, though brief, was chock full."

Franklin said there had been a plan to erect a mural to King soon after the $18 million library was completed in 1972, but there was no money for the project.

But Miller persuaded the library's nine-member board that the mural had to be done. Said Nora Drew Gregory, who heads the mural project, "He told us it was in his heart and soul."