'In Plain Sight': a photo historian takes his turn behind the camera; In Plain Sight, by Beaumont Newhall. Layton, Utah: Peregrine Smith Books. Foreword by Ansel Adams. 65 pp. $35.

There is hardly a photo historian alive who is not in some way indebted to Beaumont Newhall. Newhall was the first curator of photography at the Museum of Modern Art, directed the George Eastman House in Rochester, N.Y., for 14 years, and nurtured many a young historian of photography in his years at the University of New Mexico.

Newhall is best known for a book that began as a catalog for ''Photography, 1839-1937,'' an exhibition he organized for the Museum of Modern Art in 1937. That book, titled ''The History of Photography,'' has sold over 100,000 copies and is now in its fifth edition; no library on photography is complete without it.

Newhall has spent his life studying, writing about, promoting the work of, and befriending photographers. But ''In Plain Sight,'' which contains 59 plates of Newhall's own photographs, comes as something of a surprise.

Repeated exposure to the images in ''In Plain Sight'' suggests that the history of photography acted as a filter on Newhall's lens. The images he made at Point Lobos look like Edward Weston's work; a Manhattan skyscraper resembles a Stieglitz; and more than one photograph made in Paris has the flavor of Atget. It's as if Newhall is trying to see through the eyes of these and other photographers.

What Newhall says in his introduction tends to support this notion. ''Over the years,'' he writes, ''photography has been to me what a journal is to a writer - a record of things seen and experienced, moments in the flow of time, documents of significance to me, experiments in seeing. It has been important to me, as a historian of photography, to understand photography by photographing.''

Seen in this light, ''In Plain Sight'' stands taller. How many drama critics write plays, for example? How many art critics exhibit regularly? Newhall, even if his viewfinder is occasionally under another's influence, has produced a book that is thoughtful and elegant and the better for the knowledge behind it.