On Jan. 20, how will Americans observe the national holiday of Martin Luther King Day? Uneasily, it should be hoped.

King's life, unlike George Washington's (whose birth is also honored by a federal holiday), is contemporary. He would have been 57 this month, still fired with life's energies and still telling us in his rich metaphors that the furnaces of violence, racism and economic terror remain hot. The choices of conscience that King asked the nation and individuals to make, whether early in his career when he was the president of the Montgomery (Ala.) Improvement Association or late when he said in his last sermon in Memphis that "the nation is sick," remain the choices of today.

The overlap of issues is matched by people who were opponents of King's values in the 1960s and who, with new respectability, keep on opposing. Jerry Falwell, speaking to his Baptist congregation in Lynchburg, Va., in March 1965 said of his fellow Baptist, who was then marching in Selma, Ala.: "I must personally say that I do question the sincerity and nonviolent intentions of some civil-rights leaders such as Dr. Martin Luther King Jr. . . . and others, who are known to have left-wing associations." Barry Goldwater campaigned for the presidency in 1964, supported by many of the factions that King had to face on the streets. King said that until the defeat by Lyndon Johnson, "Goldwater was the most dangerous man in America. He talked soft and nice, but he gave aid and comfort to the most vicious racists and the most extreme rightists in America."

King gave as hard as he took. Eventually that part of his thinking -- abrasive, prophetic, confrontational -- will likely be worn into a smoothness that is no threat to the established way. The process has already begun. Last week The New York Times, in a lead editorial, came down on such cities as San Francisco for declaring themselves sanctuaries for illegal refugees from Central America. The editorial, which accuses the cities of misguidedly engaging in civil disobedience because it is a "federal function" to define the status of immigrants, cites King as the authority on breaking a law for reasons of conscience.

That he is, but is it to be imagined that King, if here today, would be opposed to the Biblically inspired sanctuary movement? Would he have closed the door of his Ebenezer Baptist Church in Atlanta to Salvadorans? Would he have told the city supervisors of San Francisco and the other cities to be quiet and report the Salvadorans because the Reagan administration orders it?

King is remembered for his oratory, which means that posterity may only see the flowery I-have-a-dream images and not his passion for specifics. The Sunday before his death, he spoke at the National Cathedral in Washington. Study peace, he told the Episcopal congregation: "There is a need for all people of good will to come with a massive act of conscience and say in the words of the old Negro spiritual, 'We ain't goin' study war no more.' This was the sermon in which, after telling of his trip to India and pursuing the spirit of Gandhi, he summarized the only option remaining: "It is no longer a choice, my friends, between violence and nonviolence. It is either nonviolence or nonexistence."

From Washington, King went to Memphis. On the eve of his death, he preached at the (Bishop Charles) Mason Temple, an African American pentecostal denomination. All of King's sides were on display in this sermon, as if he had a premonition of death and was summarizing his thinking in one final statement. He spoke of "the threats that were out . . . from some of our sick white brothers." He was "not concerned about that now. I just want to do God's will."

With wit he recalled the pre-movement days when "Negroes were just going around . . . scratching where they didn't itch and laughing when they were not tickled." He had a wry line about Sheriff Bull Conner of Selma: through nonviolence "we ended up turning Bull into a steer." Quoting Amos from the Old Testament and Jesus from the New, King called on his followers to practice a "dangerous unselfishness." Tactically they should exert the "power of economic withdrawal." For those companies that had been unfair in their hiring policies, the economic pressure was a way to "redistribute the pain."

The writings, sermons and interviews of King are being published this month in "A Testament of Hope," a 676-page work edited by James M. Washington, a New York church historian. The title could have been sharper. Why not "A Testament of Hope and Action"? But the perspective is totally accurate. Washington opens with a selection of 13 essays on nonviolence. They belong in the beginning. Nothing of King's greatness can be understood without first seeing the reasons for his absolute commitment to the belief that "the aftermath of violence is bitterness (while) the aftermath of nonviolence is reconciliation."

Had King not taught and practiced that, his national holiday on the 20th would become as hollow as the one for George Washington's birthday: an excuse for the department stores to hold a sale. King's holiday is a call to conscience, not commerce.