They are photographs of a past we thought we had lost, a world of spired wooden villages and bearded peasants with medals on their chests, of farm girls squinting in brilliant sunny snowscapes, and vast, awesome wheatfields that touch the horizon, of gilded phantasmagoric churches and the pleasant aspen-shrouded summer homes of forgotten generals and, scowling at us in his pressed rough shirt, the aged national treasure, Tolstoy himself.

It is Holy Mother Russia, Tsarist Russia, in the late decade of its life.

And it is in color.

The story of this extraordinary book, "Photographs for the Tsar," is almost as haunting as the pictures themselves, part of a collection of 2,000 slides produced in a laborious three-negative process by Sergei M. Prokudin-Gorskii. The photographer, who was also a chemist, had studied with the German Adolph Mieth and the Frenchman Edme Maumene and had gone beyond them to perfect his own technique.

Then he charmed the Tsar, Nicholas II, into letting him roam all over Russia in a special railroad car fitted with darkroom, living quarters and ice water, or in any one of three seagoing vessels, taking Russia's snapshot for slide presentations designed to impress students across the nation with their great hertiage.

Came World War I and the Revolution Nicholas disappeared along with his way of life, and Prokudin-Gorskii fled to France with his slides. He died in Paris in 1943.

The scene shifts to New York, 1946. The American Council of Learned Societies had embarked on a huge translating project, a six-volume history of Russian art, and was looking for some illustrations. The translator, Princess Marie Putiatin, happened to recall that her husband's father used to talk about a certain photographer chap he had introduced to the Tsar years ago. She seemed to remember that the man's two sons were living in Paris.

The council's director, Mortimer Graves, called Paris, found the sons, who were scraping along by printing up the slides, and talked the Rockefeller Foundation into buying the collection for $5,000. It is now in the Library of Congress.

A Russian history professor, Robert Allshouse, heard about the pictures and approached Dial Press because he had seen one of their few photo books.He had the impression they specialized in photos. They rose to the occasion, though, as they point out in the book, perfect reproduction was impossible.

Still, it's a start, as Alan Fern, director of special collections at the Library of Congress, noted. "There are several points of view possible here," he said, "architectural history, folk painting, formal painting, Russian peasant life, a history of photography no one person could do it all. We're delighted this first bunch of pictures is published. We only wish they had been given some sort of designation for reference."

In places, he added, the color work could be improved. Some pictures are out of register, there is bleeding and soft focus and evidence of shrinkage. It could take years of fiddling to get the photos just right, since each one must be printed three times, in red, yellow and blue, in perfect alignment.

"This opens the door for much more work to be done on the collection," Fern said.

The man who made it all happen, Mortimer Graves, reached at his home in West Newbury, Mass., said he hasn't seen the book yet. "It costs $35," he grumbled. "I can't afford it."

The real problem in getting the glass slides published, he said, was the act of faith it took to perceive their potential. For all you see are three black-and-white repititons of a subject, one light, one medium and one dark. The magic doesn't happen until you expose them together.

The 216-page book contains many uncolored pictures, too. One of the most impressive is the towering ruins of the Mosque Bibi Khanum, built by Tamerlane in 1400. Surrounded by peasant hovels and modest commercial buildings, this grandiose wreck says all that need be said about empires.

But there are other photos here that stay with you longer, scenes from a vanished landscape stretching from the Caucasus to Samarkand. One small color picture, sharp and glinting with a swift-flowing river, shows one Pinkhus Karlinsky, keeper of the lock at Chernyakhovsk for 66 of his 84 years. He stands at attention on the gate, pole in hand, greatcoat buttoned trimly, black visored cap contrasting with white beard, his broad Russian face full of pride and fear, warily greeting an unknown century.

Prokudin-Gorskii told his family he left behind 10 color photos of the Romanov royal family when he took off from Russia in 1918. The only one he saved was an appealing snap of Tsarevitch Alexis, that sad little victim of history. As for the others, all we know is that they are hidden somewhere, probably in Leningrad. Maybe they'll turn up one day.