Perhaps the most impressive thing, after the numbers, was the silence -- 100,000 people, gathered together in one of the noisiest cities in the world, some bowing their heads, some quietly crying, but none speaking, so that all you could hear, during the 10-minute vigil in the enormous park, were the whir of the police helicopters overhead and the continuous camera shutter clicks of the ubiquitous press.

That stillness was broken, as the announcer had said it would be, by the song that has become John Lennon's song after death, "Imagine," and with it a large cheer -- a good send-off, more befitting a wake than a vigil.

"Thank you, John Lennon," yelled a kid in the first row behind the police barricades, "Thank you!"

Lennon is gone, shot to death last Monday outside his Manhattan home. There was no funeral. But, in keeping with the wishes of his widow, Yoko Ono, that fans at 2 p.m. today "pray for John's soul," he was mourned across the world. There was a memorial concert attended by 30,000 in the Beatles' hometown of Liverpool -- a concert marred by violence and widespread injuries -- there were, as well, a park gathering in Chicago of about 2,000 people, and a convention in Boston. But by far the largest gathering was here, in New York's Central Park, where thousands, carrying flowers and placards, bundled in blankets and heavy coats, braved freezing weather to listen to a recorded concert of classical and Beatles music.

For the most part quiet and peaceful, the gathering was marrred by one incident after the vigil was over: Not quite an hour after the 10 minutes of rememberance for Lennon, as people started to disperse, two young men got into an argument, then a fist-fight. A short time later, according to police, one of the men returned with a small caliber gun, not unlike the one that killed Lennon, and shot the other in the chest. The alleged assailant, identified as a 22-year-old resident, has been charged with attempted murder.

There was also, throughout the day, a bit more commercialism than some might have preferred. At the entrance closest to the park, a half-dozen impresarios were selling Lennon buttons, three for $5; or "The John Lennon Tribute Collector's Issue" for $2.50. Within the park, near the band shell where the concert was held, a few more tradesmen were hawking "The Legend Lives" T-shirts for $6, and large, framed pictures of the Beatles, 200 of which, at $12 apiece, were sold within the hour.

But that aside, it was a tranquil afternoon given to mourning and memories. As they did throughout New York State, flags flew at half-staff, and in Central Park, many of the mourners carried flowers or brought candles.

Though New York Mayor Ed Koch was in attendance, and actress Jane Fonda and her husband Tom Hayden were in the crowd, there were no speeches and few announcements. The mayor, arriving in a turtleneck sweater and sheepskin coat, did use the opportunity to tell reporters who mobbed him that there would be fewer crimes of this sort were the nation to adopt strong gun control rules. (Earlier in the day, several city representatives including New York City Council President Carol Belamy and Reps. Elizabeth Holtzman, Ted Weiss and Jonathan Bingham, had released a statement urging the incoming Reagan administration to adopt a strict gun-control law.)

Koch also, in answer to questions from a somewhat belligerent British reporter, insisted that no, Lennon's murder here did not reflect badly upon New York. But he sidestepped making any lengthy remarks about Lennon, and when a reporter asked what he would be thinking throughout the 10 minutes of silence, he gruffly declined to comment.

"That's a very personal matter and I don't intend to share it," he said.

It was a personal matter, too, for thousands of mourners who flocked to silent vigils across the country and throughout the world.

"People just need a focal point for their sense of loss," said Bob Linden, program director of KEZO-FM, in Omaha, Neb., as the station sponsored a memorial that drew 2,000 to Rosenblatt Stadium.

Radio stations in many countries observed 10 minutes of silence, while others played special programs of Beatles music.

"I think it's great that all over the world, in unison, there was silence," said Paul Curry, one of 600 people who attended a vigil in Los Angeles' Griffith Park.

"It was kind of eerie," said Bill Cates, one of 2,000 who joined a memorial at Boston's Copley Square. "All I heard was the flag flapping . . . . It was kind of sad."

In Washington, about 70 American University students, most of whom were only four when the Beatles first appeared on the Ed Sullivan Show in 1964, gathered in the chill in front of the campus' Kay Spiritual Center for a moment of silence in Lennon's memory.

In Melbourne, Australia, several thousand people poured into the city square at 6 a.m. Monday local time -- simultaneous with 2 p.m. EST -- to watch a giant video screen display of a Beatles concert.

More than 1,000 people took part at the Statehouse in Columbia, S.C.; 1,200 at the Statehouse in Columbus, Ohio; 3,000 at the site of the 1962 World's Fair in Seattle; 1,000 on Cricket Hill along Chicago's lakefront; 600 at Louisana State University in Baton Rouge; 3,000 at Miami's Bicentennial Park; 800 at Salt Lake City's Memorial Grove Park.

About 4,500 people attended a vigil at Red Rocks, a natural red sandstone amphitheater in the Rocky Mountain foothills west of Denver. The Beatles had played a concert there in 1964.

In Liverpool, where the mop-haired quartet grew up, more than 30,000 people, many in tears, flooded into a square outside St. George's Hall for a seven-hour concert of the group's music. Hundreds had camped all night on the steps of the hall in near-freezing weather.

About midway through the concert, a band started playing non-Beatles numbers, angering many in the crowd who clambered onstage apparently to vent their displeasure. Police said about 100 people suffered injuries, mostly minor, or fainted, and three were taken to hospitals.

The commemoration here in New York, beginning shortly after a concert of recorded music, was simple to the point of not being a program at all. There was a large picture of Lennon, in a sleeveless "New York City" T-shirt, center stage of the band shell surrounded by flowers; there were occasional announcements to the cooperative crowd. Just before 2 p.m., when the vigil was scheduled to start, came a recording of "Give Peace A Chance," an old anti-war Lennon song that seemed to carry a special meaning for the crowd.

Arms linked, hands raised in the old peace sign "V", they sang along with the music under the gray New York skies. Mourners behind the barricades, mourners huddled with their families under blankets on the grass, mourners who had climbed the trees, they all flashed the "V" and sang along -- even the mayor, many in the press, and, here and there, a policeman. Over and over again, the same crescending line: "All we are saying, is give peace a chance." A curious sight in 1980; a ghost of the antiwar days, the peace and love days of '68 and '69.

Then the music stopped and the vigil began -- 10 minutes of silence in a cold, windy park. Then -- the silence over -- another Lennon song, "Imagine," the crowd singing along again, the song more triumphant than sad.

. . . Nothing to kill or die for And no religion too Imagine all those people Living life in peace you may say I'm a dreamer But I'm not the only one I hope someday you'll join us And the world will be one.

The crowd began to disperse. Some simply left the park, some marched across town to gather together outside John Lennon's home. In the group remaining, a teen-age boy waved a sign: "Can you see how stupid violence is?" r