On April 22, 1935, a tourist from New York named Fred Hill waded through the crowd at the White House Easter Egg Roll, pointed his movie camera at the South Portico and captured seven seconds of history.

As Hill filmed, President Franklin D. Roosevelt, who had been disabled by polio 14 years before, emerged and — with the help of a cane and his bodyguard — walked unsteadily to wave to the crowd.

Walking was something Roosevelt did with great difficulty. He looked awkward and vulnerable, and he was rarely filmed doing so.

On Wednesday, the Franklin D. Roosevelt Presidential Library and Museum is expected to unveil the newly acquired Hill footage, which it says offers a fresh, remarkably clear glimpse into one of the great secrets of FDR’s public life.

“When I saw [it] . . . I gasped,” Paul Sparrow, the director of the library in Hyde Park, N.Y., said last week.

“I had never seen this footage before, and we had a sense that no one had ever seen this footage before,” he said.

Sparrow said newsreel cameramen were warned against filming FDR while he was walking, lest his disability be shown. The president could walk only with heavy leg braces and assistance, and only for short distances.

And even then he walked with a stiff, unnatural gait.

“Mr. Hill . . . didn’t know the rules so he just” ran his camera, Sparrow said.

The film of Roosevelt continues for another 30 seconds as the president’s bodyguard, former New York City policeman Gus Gennerich, steps into the background.

The president, then 53, wears a double-breasted coat and pocket handkerchief. He strides into the sun, hooks the cane over the balcony railing and greets the crowd.

He smiles and waves, always keeping one hand on the railing. First lady Eleanor Roosevelt stands beside him, along with two of her nieces, Diane Roosevelt, 8, and Amy Roosevelt, 6, according to Roosevelt biographer Geoffrey C. Ward.

With a final wave, Roosevelt slips the cane off the railing with his right hand. Gennerich reappears at his left side, and the group walks back across the portico.

A frame from the previously unseen film showing Roosevelt walking. (Fred Hill/Franklin D. Roosevelt Presidential Library and Museum)

“I was dazzled,” Ward said of the new footage. “It’s by far the clearest image I’ve ever seen of something that’s obsessed me for 20 years.”

The silent 16mm film, in black and white, was donated to the library, which is a part of the National Archives, in December by Richard Hill. He is a lawyer in Reno, Nev., and Fred Hill’s grandson.

The film was digitized for the library at a private laboratory in Rockville, Md.

Richard Hill said his grandfather was the bookkeeper for the family business — Hill and Sons, in Brooklyn, which had been founded as a horse wholesaler in New York — and later got into real estate in Nevada.

The family wound up running a dude ranch in Reno, where his grandfather made dozens of home movies. He said he discovered the Roosevelt clip in the 1980s by accident when a local TV station was seeking historical footage of old Reno.

Hill, 66, said in a telephone interview that he had offered the clip to the library in the 1980s, but he lost interest and didn’t follow up. He said he made the donation last year because he is getting older and it seemed like the right time.

“I’ve kind of jealously guarded this stuff,” he said. Now, it “needs to go where it belongs . . . It’s an important part of history that almost got away.”

Roosevelt was a rising figure in Democratic Party politics in 1921. He was 39 and had been assistant secretary of the Navy and a candidate for vice president.

But that summer he was stricken with polio and lost most of the use of his legs.

His courageous recovery, and efforts to conceal the extent of his disability, are rich chapters in American history.

He mostly used a wheelchair to get around, although he often had to be carried by aides and sometimes crawled from one room to another on the floor, according to biographer Ward, who also was stricken with polio.

Roosevelt fought to be able to walk.

“I must give principal consideration for at least 2 years more to getting back the use of my legs,” he wrote a friend in 1926 about his political future.

“Up to now I have been able to walk only with great diff. with steel braces and crutches, having to be carried up steps, in and out of cars, etc. etc. Such a situation is, of course, impossible in a candidate,” he wrote.

It took him seven years but he eventually managed to master a stiff, ungainly walk.

He returned to public life, was elected president four times, brought the country out of the Great Depression, and led it during most of World War II.

Yet he was careful to hide his disability.

“No movies of me getting out of the machine, boys,” he told waiting cameramen as he was about to get out of a car the day he was elected governor of New York in 1928, according to Ward.

The cameramen obliged.

“People didn’t want him to be handicapped,” Ward said. “We were in the middle of a depression. They wanted their president to be a vigorous, able person, and he wanted to fulfill that role.”

Of the hundreds of photographs taken of him, only a handful show him in his wheelchair, Ward said.

And footage of him “walking” is just as rare.

“There are a number of very short, very blurry shots,” Ward said in a telephone interview last week.

Four years ago, seven seconds of amateur film surfaced of FDR making his way up a ramp at Washington’s old Griffith Stadium for the 1937 baseball All-Star Game.

In August 1933, a doctor filmed him walking, again holding Gennerich’s arm and using a cane, at a public event in Poughkeepsie, N.Y. The clip lasts six seconds.

Brief, partially obscured footage exists of him walking at Mount Vernon in 1939, at his third inauguration in 1941, getting off a train in Boise, Idaho, in 1937, and at other public appearances in New York, according to the FDR library.

The known clips appear to total less than a minute.

In Fred Hill’s, “you really get to see . . . [FDR’s] gallantry and also you get a pretty good glimpse of the way it’s orchestrated,” Ward said.

Gennerich, as well as being FDR’s bodyguard, was “his enabler, that allowed him to walk,” Ward said. “Roosevelt sometimes used his sons, who were also big guys, to do that. But Gennerich was the daily guy.”

“It’s like choreography,” Ward said. “You watch him bring Roosevelt up to the railing. The minute he gets to the railing, he steps way back and then he goes back behind [a] pillar.”

“And he doesn’t come out again until” Roosevelt is ready to leave, Ward said.

The president had “this amazing ability to look as if absolutely nothing was wrong,” he said. “When you look at him, he looks like the most carefree man in the world.”

But sometimes, the choreography didn’t work.

In June 1936, Roosevelt almost fell at the Democratic National Convention in Philadelphia at the University of Pennsylvania’s football stadium, Franklin Field.

There were 105,000 people present, according to news reports.

“Spotlights followed him as he made his halting way toward the microphones . . . to accept his renomination for the presidency,” Ward wrote in his 1989 book about Roosevelt, “A First-Class Temperament.”

Holding a cane with his right hand and the arm of his son, James, with his left, he stopped to greet someone in the crowd. He lost his balance, the brace on his left leg gave way and he started to go down.

But Gennerich was near and caught the president under the arm just in time. (Five months later, Gennerich would die of a heart attack on a trip with Roosevelt to Argentina.)

“There I was, hanging in the air, like a goose about to be plucked,” Roosevelt told reporters later. “But I kept on waving and smiling, smiling and waving.”

There is no known film of the mishap.

And the speech he gave minutes later “was one of the most memorable addresses of his life,” Ward wrote.

“There is a mysterious cycle in human events,” Roosevelt said. “To some generations much is given. Of others much is expected. This generation of Americans has a rendezvous with destiny.”