ASHINGTON — During the six weeks I spent reading Justice Harry A. Blackmun's collected papers in the Library of Congress, I often felt that I had left the familiar surface of the earth and plunged down a rabbit hole into a separate world.

It wasn't only that after covering the Supreme Court's public face for many years I was now immersed in the court's private life. That was the whole point, after all. It was why I was there, with the permission of the Blackmun family, who gave The Times an opportunity to examine the papers in the quiet of January and February before the library opened them to the world on March 4, the fifth anniversary of Justice Blackmun's death.

No, I felt I had entered another world because, in a literal sense, I had. The reading room of the Library of Congress's Manuscript Division was unlike any place I had ever spent time. Walking in there was like entering the temple of a sect I barely knew existed: before approaching the precious documents that are the original source material of the country's cultural and political heritage, a researcher must first strip bare, or nearly so.

All personal possessions, including jackets with pockets, are locked away. The only paper and pencils allowed are those the staff provides. Laptop computers are permitted, but they must be opened for inspection upon entering and leaving. Anyone leaving for a moment, even to make a telephone call, is checked in and out by a guard much more vigilant than any high school hall monitor.

It sounds oppressive, but it isn't, really. The rules, the reasons for which are completely understandable, help create a kind of community of worshipers at the shrine of the original document. And the shared enterprise of reading other people's mail - whether it is Walt Whitman's, Margaret Mead's, Sigmund Freud's or Harry Blackmun's - is mesmerizing. On several Saturdays, I went to the library to check on one or two items, only to look up and find that hours had somehow slipped by - a common experience, I learned.

The Blackmun papers, more than half a million items, are contained in 1,585 boxes. Those numbers were not quite real to me until, in late December, I received the index to the collection by e-mail. It printed out to more than 300 pages. I printed copies for myself and Francis J. Lorson, the recently retired chief deputy clerk of the Supreme Court, who had signed on as my research assistant.

As we sat in the dining room of Frank's Georgetown town house with the index spread out on the table, the two months that had loomed before us now seemed pitifully short. We each searched for a way to express without undue panic what we were both thinking: now what? Even limiting our search to the opinions that Justice Blackmun wrote over his 24 years on the court would not be limited enough. We drew up a road map, listing cases by category, and got ready to plunge into what looked like very deep water indeed.

We expected the abortion and death penalty files to be both interesting and important, and of course they were. But the material on Chief Justice Warren E. Burger was completely unexpected in its range and its revealing nature. There were two main collections of correspondence between the two friends, one from their shared early adulthood and the other from their service on separate federal appeals courts.

During the 16 years they spent together on the Supreme Court (from Justice Blackmun's arrival in 1970 until Chief Justice Burger's retirement in 1986) they grew apart in both substance and style. The chief justice proved to be a heavy-handed manager of an increasingly resentful group of colleagues, while Justice Blackmun moved rather quickly out of his shadow to assert his independence and increasingly liberal views. By the end, the two were communicating, if at all, through crabbed memos.

Having known Chief Justice Burger - remotely, to be sure, but I covered the court during seven years of his tenure - I never would have imagined him as the writer of these self-appraising, importuning, sometimes poetic, often passionate letters to the friend he turned to for professional advice and emotional reassurance. Reading them was like entering a Victorian epistolary novel. Of course, I knew in advance the sad final chapter of estrangement, but the sense of loss and of mutually dashed expectations was palpable in the bitter silence that followed.

The Burger letters also pointed me to valuable information elsewhere in the collection. Had I not come upon Harry Blackmun's 1967 letter to Warren Burger expressing deep regret at having suppressed his real views against the death penalty in an opinion he had just written for the appeals court upholding a death sentence, I never would have called for the file on that case, Pope v. United States.

The file revealed what I came to think of as Justice Blackmun's "Rosebud,'' at least as far as the death penalty was concerned: the crucial incident, retrospectively, that made sense of all the rest. It took him an additional 27 years, but the moment came, almost exactly 10 years ago, when he gave himself permission to speak his mind at last, explicitly renouncing the death penalty. Perhaps it freed him to retire, which he did, at 85, a few months later.

In addition to the serendipitous discoveries, the project gave Frank and me the chance to satisfy our curiosity about particular cases. Sometimes we liked what we found, and sometimes we were, frankly, a bit sorry to have found it. In the former category, definitely, was "Poor Joshua!'' - Justice Blackmun's exclamation of empathy and dismay in a dissenting opinion in a 1989 case about the rights of a little boy whose father had beaten him nearly to death. This was such an unusual expression of judicial sentiment that I had always wondered where it came from.

It came, it turned out, directly from Harry Blackmun, unmediated by any law clerk, unrevised by any second thoughts. In the file on the case, DeShaney v. Winnebago County, is Justice Blackmun's draft of the dissent, in his tiny handwriting on lined paper, almost precisely as it was later published.

On the other hand, one of Justice Blackmun's most famous passages, from his endorsement of affirmative action in the Bakke case, turns out not to have been so original. In his separate opinion in that 1978 case, he wrote: "In order to get beyond racism, we must first take account of race. There is no other way.

In his file on the Bakke case is an article on affirmative action by McGeorge Bundy, published in the November 1977 issue of The Atlantic Monthly. In the article (which Justice Blackmun marked "Read 5/6/78'' - in other words, as he was preparing the opinion that was issued the next month), Bundy, the former national security adviser and Harvard dean, wrote: "To get past racism, we must here take account of race. There is no other present way.''

There is no footnote to this source in Justice Blackmun's opinion. Trying to trace the opinion back through its various drafts, we never could reach a conclusion on whether the lapse was Justice Blackmun's or a law clerk's. Nor did we learn whether Mr. Bundy, who died in 1996, ever commented on the borrowing; it may well be that he was terrifically pleased to have endowed the affirmative action debate with such a pithy phrase.

As the project moved to the writing stage, I found that I missed the daily ebb and flow in the reading room: the man with the long gray ponytail researching the Civil War ("I'm working on a new angle''), the dissertation writers, the people doing family history, but most of all the helpful and enthusiastic reference librarians who work there. One, Jeffrey M. Flannery, took Frank and me on a backstage tour through the shelves one quiet afternoon. There were George Washington's diaries; the voluminous files of leaders of the civil rights movement; the papers of Edna St. Vincent Millay; the papers of Frederick Douglass - 11,000 collections in all.

"When I go home at night,'' Mr. Flannery said, "I like to think that they're all in there talking to each other.''