Word spread quickly around the hidden community of the Library of Congress: Baker got a Pulitzer!

And for once Leonard S. Baker wasn't even there. He was at home taking phone calls about his book, "Days of Sorrow and Pain: Leo Baeck and the Berlin Jews," which has indeed won the 1979 Pulitzer award for biography.

After eight years, Baker is one of the oldest inhabitants of a curious little world: the desk-holders of the library.

There are 200 study desks scattered around the stacks, available free to serious scholars working on doctoral theses or books. You can bring a typewriter, even a tape recorder with earplugs, and you can keep books there overnight; a privilege not extended to the ordinary toilers in the main reading room who must turn in their books at the day's end and start all over the next morning.

An elite group, these scholars. MA candidates aren't allowed in-all they can manage is a private shelf for their books. Some desk-holders stay just two or three months, but the average is nearly three years. The waiting line is daunting, especially in summer when the place is packed with graduate students released from teaching jobs.

Only about five people have been there longer than 10 years, with breaks now and then for research elsewhere, and "a couple of people have been here forever," one library official muttered.

Productive people, most of them. Many work a 40-hour week, and nobody knows just how many books have come out of those little cubicles buried deep among the rows and rows of shelves. Alex Haley worked there, and so did Herman Wouk and other famous writers.

Baker himself worte four of his seven books at the library.

"It wasn't easy, breaking away from newspapers," he said."Fourteen years ago yesterday" he quit Newsday to write a book based on his Washington bureau experiences. It was a study of the Johnson vice presidency, and he followed it with a steady series of works on politics and law.

"While I was doing the biography of John Marshall I got interested in the law as an institution and how society depends on it to hold itself together. I knew about Baeck and I began to wonder what happens to a law-abiding group like the German Jews when they're suddenly denied the protection of the law."

So Baker started on a five-year odyssey that took him to 10 countries for at least 100 interviews and gave him a stack of note cards as high as your chin.

"I do all my research first, and sometimes it's hard to get a book contract because they always want a chapter to two. But I spent three years putting it all on the cards and shuffling through them over and over, organizing, getting new perspectives and connections. Basically I'm a fast writer, but with this one I did four major drafts and spent almost a year reworking it. It shows."

Thinking of Baeck, the leading rabbi of Berlin and a beloved Jewish theologian who not only saved thousands of Jews from the Holocaust but also consoled, served and led them at the camp-ghetto of Theresienstadt, where he was sent to age 69, the author dedicated his book to the memory of his own step-grandfather, Rabbi Abraham Baker.

When the dust settles, the 48-year-old Baker will head back to the stacks. So far, he has had to work part-time as a writer-editor for various government agencies because his other books don't bring enough to support him and his writer-wife and two children. It would be nice, he said, if the prize-winner turns into a bestseller. But one suspects that he would keep writing anyway. His new project is set in the 18th century.

Just about a year ago, the library was delighted to learn, the hidden scholars formed an organization, as Americans invariably will. Now they hold seminars and regular colloquia where they tell each other what they're doing. It's much jollier that way. They aren't really troglodytes, after all.

Who knows, maybe they'll give Baker a party when he gets back. CAPTION: Picture, Leonard S. Baker; by John McDonnell-The Washington Post