NEW YORK, OCT. 9 -- John Lennon's worldwide message of peace was delivered today as his song "Imagine" was played simultaneously for 1 billion people in 130 countries to celebrate what would have been his 50th birthday.

"A dream we dream alone is only a dream, but the dream we dream together is reality. Happy birthday, John. The world is better today for sharing a time with you," Yoko Ono said at a United Nations ceremony before the playing of "Imagine."

The former Beatle, slain in 1980, issued a call for harmony himself in a taped message that served as an introduction to the music.

"We all want peace, whatever sort of job we have. ... Think of your children. Do you want them to be killed or don't you? And that's the choice we have in front of us. War or peace," said Lennon, whose son Sean turned 15 Tuesday.

None of the other Beatles was at the United Nations, but a tribute came from Lennon's former songwriting partner, Paul McCartney, who released a live version of the Beatles' tune "Birthday." The song, originally on the "White Album," was the first Lennon-McCartney single released after the Beatles broke up in 1969.

Other observances were held from Liverpool, England, to Moscow to Los Angeles. In Lennon's hometown in England, fans gathered at the former site of the Cavern Club, where the Beatles were discovered.

More than 1,000 radio stations and networks from 50 countries broadcast the 10-minute event. U.S. armed forces television and radio beamed it to 80-plus other countries. MTV televised the "Imagine" video in 25 countries, said Andrea Smith, a spokeswoman for the network.