Harry Truman was president, daily papers cost three cents and life was sweet when Jimmy Castro opened a newsstand on 17th Street NW, just one block from the White House.

It was a fine location from which to view politicians, potentates and humbler folk, and in fair weather and foul, his customers could always count on a quick smile and a soft greeting from the vendor with the Edward G. Robinson looks.

Washingtonians clustered around Castro's stand to watch President Kennedy's funeral procession creep down Pennsylvania Avenue 20 years ago and stood in a block-long line to buy a paper from him 11 years later when President Nixon resigned.

Only last fall, when diabetes and a serious foot infection sent Castro to the hospital, was his 34-year love affair with his native city ever tested.

But the capital returned his admiration, showering its senior "corner boy" with gifts and mail.

"Dear Jimmy," wrote one fan and neighbor, "I was sorry to learn that you have not been feeling well, and I want to take this oppurtunity to tell you that I am thinking of you.

"I hope you are back on your feet and back on the corner again soon," the letter said. "You have many friends pulling for you and you can be sure that Nancy and I are among them."

Bouyed by the words from President Reagan and 80 other letters, Castro, 66, made it back to his corner last week, rolling around a battered metal stand with the gait of a former sailor.

"Glad to see ya back, Jimmy. You're lookin' grand," said one pinstriped lawyer, pressing a $10 bill into Castro's hand before rushing into a nearby office building.

"Where you been, Jimmy?" asked a woman in her 20s as she plopped down a quarter for that morning's paper.

"Been sick," Castro said. "I'm still weak but better now."

A liking for "the bottle" and long hours in bone-chilling rains sent him to the Veteran's Medical Center on Irving Street NW in November, Castro said between sales last week. His doctors prescribed a new diet and medication for his diabetes and amputated the badly infected toes on his left foot.

"I'm takin' strict care of myself now," said Castro, who was raised in Foggy Bottom. "Doctor says I got to."

Castro is one of about 10 independent street vendors left in the District, most of whom are elderly men who sell newspapers to supplement their pensions.

"The corner boys are a dying breed, a dying generation," said Mike Devlin, a distributor who supplies Castro and others with newspapers.

Four vendors died in the past four years, and the meager pay makes replacements hard to find, Devlin said. A vendor makes about five cents on every 25-cent paper he sells; a good day means $15 in take-home pay.

Castro, whose first name actually is Manuel, started hawking newspapers as a boy, in the heyday of Washington journalism when readers could choose from a variety of morning and afternoon dailies and the pages sang with the breezy columns of Arthur Brisbane and Heywood Broun. When World War II came, Castro, the son of a Filipino immigrant, saw combat in the Pacific and North Atlantic duty in the Coast Guard.

He was discharged after "seven years, two months and five days" in the service and opened a newsstand because it was steady work and brought him into contact with people from every walk of life. "I like the newspapers, all of 'em," Castro said, fingering one of the 10 different dailies he sells.

"I'm not going to pick a favorite," he said, "because they're all my bread and butter."

Castro's stand at Pennsylvania Avenue and 17th Street NW was his window on the comings and goings of eight presidents. Truman would wave his cane at him on brisk walks around the White House, and a bullet fired in the assassination attempt on Truman at Blair House ricocheted over Castro's newsstand and hit the old Whalen Drug Store 10 feet away.

"I was away on business at the time, so there was never any danger to him ," Castro said.

In 1957, District police charged Castro and two other men with running an illegal numbers game, but Castro never went to jail, he said. He doesn't talk much about the incident and rarely plays the city-run lottery.

Castro's is the second most profitable corner in Washington (Connecticut Avenue and K Street NW is the leader, distributor Devlin said) and his many customers rallied around him when he went into the hospital.

Columnist Art Buchwald and Newhouse News Service librarian Donna Maze, both customers of Castro's, passed the hat for him in their offices at 1750 Pennsylvania Avenue, near the newsstand.

They raised nearly $200 and bought a bathrobe and thick sweater for him. Another Newhouse employe, White House reporter Loye Miller, arranged Reagan's get-well card, while 80 other regulars sent notes to Castro in the hospital.

"Yeah, it was nice, real nice, to hear from everyone," Castro said as he lugged a two-foot stack of papers to his stand.

"But I don't know how long I'm gonna do this, you know? The winters, they're cold. I may just want to sit back and take it easy."