THE EVER-SENSITIVE relationship of presidents and Supreme Court justices is back in the news, thanks to Robert J. Donovan's new Truman biography. But one extraordinary episode in that strange and unstructured interplay -- an episode involving Truman and the late Justice William O. Douglas -- apparently ecaped Donovan's attention, as it has other recent historians and biographers of the president and the justice.

The massive files of the Harry S. Truman Library at Independence, Mo., contain a remarkable two-page, longhand letter from Justice Douglas to President Truman, dated July 1, 1952, offering to resign his seat on the Supreme Court to campaign for Truman, should the president agree, as Douglas strongly hoped he would, to run for another term in the White House.

That Douglas, his periodic denials to the contrary, had long been interested in the highest national officce, has been widely accepted for many years. In 1944, for instance, he was the receptive liberal choice for vice president, to succeed Henry A. Wallace, only to be passed over in favor of Sen. Harry S. Truman of Missouri.

In 1948, Truman, fighting for his political life, asked Douglas to be his running mate, and was apparently deeply hurt and displeased when the justice refused the offer.

In 1952, it was Douglas who took the initiative.

Truman's dramatic announcement, to a stunned Jefferson-Jackson dinner in Washington, on March 29, 1952, that he would not seek another term, threw the Democrats, already embattled, into disarray.

Truman himself reportedly favored Chief Justice Fred Vinson or Gov. Adlai Stevenson of Illinois, who, in turn, seemed to favor W. Averell Harriman, former U.S. ambassador to the Soviet Union and secretary of Commerce.

The Republicans, in turn, were bitterly divided between General Dwight D. Eisenhower and Senator Robert A. Taft of Ohio.

On the eve of the Republican convention in Chicago, its ultimate outcome still in doubt, Douglas sent the president a letter from his favorite Pacific Northwest mountains, where he had gone to spend part of the summer.

Written on letterhead "Supreme Court of the United States -- Chambers of Justice William O. Douglas," the letter must have stunned and surprised Truman when it was received at the White House on July 5, 1952, as it still amazes today:

"Dear Mr. President --

"There were some things I wanted to tell you before I left Washington, D. C. I planned to so at Supreme Court Justice Hugo Black's party. But I was running a fever that night -- and I had an awful headache. I slipped out because I was sick. You were away when I left for the summer. So I did not have a chance to pay my annual visit to see you, to unburden myself, and to say goodbye.

"I believe you know that I have no political ambitions. So what I have to say carries no selfish implications. If it turns out that you are in the race this year and need me to help you, all you have to do is to let me know. The world situation is desperately critical -- as you know better than anyone, my fears would mount greatly if any of the Republicans in the limelight were at the helm. I feel that the situation may develop so that you will have to run again. I do not want anything for myself. But the danger to the country is so great that I would gladly leave the Court and stump for you. That is the substance of what I wanted to tell you in person.

"One more thing -- somehow or other I hope you can get some cool country or mountain air this summer and a bit of vacation out of your crowded calendar. God bless you!

As ever

Bill."

Truman's response to the Douglas letter is not known, but there is no evidence that he seriously considered it.

Still, the Douglas letter -- which he apparently never mentioned to anyone in later years and word of which came as a complete surprise to a number of eminent lawyers and law professors, including old friends and students -- is bound to raise a number of tantalizing questions.

What, for instance, led Douglas to extend the unprecedented offer in the first place? especially since he made no secret of the fact that he was of two minds about Truman. He liked the president personally, and supported much of his domestic program, but on foreign affairs they parted company. As Douglas wrote later -- in his Supreme Court memoirs, published after his death in late 1980 -- "I always realized his abysmal ignorance of what actually went on in the world", adding that "One alarm that . . . I felt was the manner in which Truman miltarized the nation. . . . He greatly conditioned the American mind to think in terms of military solutions to problems of Communism."

Second, what would have been Douglas' likely place in the history of the Supreme Court had he resigned after only 13 years on the tribunal, instead of continuing for another 23, until November 1975, by which time he had become, by virtual common consent, not only one of the outstanding justices in the entire history of the court, but also the longest in point of service.

Third, did Douglas in 1952 possibly want the vice presidential nomination after all, and would Truman, had he been willing to run once more, have been prepared to accept Douglas as his running mate, knowing, as he doubtless did, their fundamental differences on foreign affairs?

Finally, what of the possible consequences for the Democratic Party and the course of American history, at home and abroad, in 1952 and after?

Could a Truman-Douglas ticket possibly have defeated Eisenhower and Richard Nixon? And in the event of his probable defeat, what of Douglas' political prospects in 1956 and 1960?

And what might then have become of men like Stevenson, John F. Kennedy and Lyndon B. Johnson, waiting in the wings?

For if Douglas's offer to resign his Supreme Court seat remains extraordinary 30 years after, so are its possible implications for recent American history.