Samuel Zanoff, who had photographed every president from Woodrow Wilson to Richard Nixon as chief photographer for Harris & Ewing, died of cancer Wednesday at the Randolph Hills Nursing Home in Wheaton. He was 91.

Described as one of the country's best potrait photographers, Mr. Zanoff had worked for Harris & Ewing for 42 years, retiring in 1967 at the age of 80. He had captured the powerful, the rich, and the eminent in dignified post worthy of their stature.

"They were all friendly," he once said, "but they didn't really have much to say, except Mr. Truman." President Harry S. Truman was Mr. Zanoff's favorite because he was the "friendliest" person to photograph. "He keep talking and kidding about almost anything," Mr. Zanoff said. "He seemed to be relaxed and enjoying himself."

Mr. Zanoff enjoyed telling stories of his photo sessions with official Washington. The presidents he photographed never were vain about the pose, he once said. They didn't ask to have their "best" profile showing. in fact, President Calvin Coolidge liked his freckles and didn't want them removed by the retoucher, and President Franklin D. Roosevelt didn't want the mole on his cheek painted out, according to Mr. Zanoff.

Photogenically speaking, Mr. Zanoff thought Roosevelt was the best president. "He had a wonderful face, the structure," he once said. President Warren G. Harding also was one of Mr. Zanoff's favorites, although he didn't say very much. "He was a very nice, a very fine gentleman," Mr. Zanoff said.

One anecdote Mr. Zanoff was fond of relating was the visit of President Herbert C. Hoover, one of only two presidents who went to the studio to have their potraits made. Mr. Zanooff recalled that President Hoover would not look at the camera until Mrs. Hoover, who was with him, said, "Dear, it's time to get your eyes off the floor."

The other president to be photographed at the Harris & Ewing Studio, which had a reputation for formal, elegantly finished potraiture, was President Coolidge. When the studio opened its new luxurious headquarters at 1313 F St. NW, President Coolidge volunteered to come down and be the first one photographed there. The usual procedure was for the photographer to go to the White House.

Mr. Zanoff's daily routine of giving orders to the nation's most prominent men and women usually began with "smile" and "relax" and "look natural," as he got ready to snap the shutter. He once confided that his time-tested formula for relaxing his well known subjects was to ask where they grew up.

His photo sessions appeared in formal because the pictures had to be taken with an alloted time - usually short. "We never have time really to pose them," Mr. Zanoff once said. (I would) "arranged their hands and adjust their coats, that's about all."

He once told of trying to remove a curl of hair from Supreme Court Justice Harlan F. Stone's forehead.

"When I was photographing Justice Stone, a curl of hair hung down in his face. So I eased over and said, 'Excuse me, Mr. Justice, er-ah, I mean this piece of hair here' - and I tried to push it back off his forehead. 'Don't do that!' Stone stopped me. 'I should think you'd know by this time, Zanoff, that's my trademark!"

Mr. Zanoff began as a photographer's apprentice some 75 years ago in a small town on the Black Sea in the Georgia area of Russia, where he was born. He had been snapping pictures, printing and retouching them. He came to Washington in the early 1900s and worked at Towles Studios for about 20 years before joining Harris & Ewing in 1925.

Harris & Ewing went out of business in February, 1977.

Others who sat in front of Mr. Zanoff's camera over the years included Gen. John pershing, John Foster Dulles, Supreme Court Chief Justice Warren, Nelson Rockefeller and Britain's Field Marshall Montgomery. On photographing former president Richard M. Nixon, Mr. Zanoff once said, "Nixon has a strong face."

Commenting on his photographic career, Mr. Zanoff has said, "I haven't regretted one minute of it. It's a wonderful job.

He is survived by his wife Leah, of the home in Rockville, two daughters Clara Cox, of Bethesda, and Rose Koenick, of Gaithersburg; a son Herbert, of Chevy Chase, four grandchildren and 11 great-grandchildren.