You don’t have to be able to read music to write it. Just ask Paul McCartney – or the kids from PS 199 on the Upper West Side. With a little help from their friend – composer and New York Philharmonic bassist Jon Deak – they composed “The New York Fanfare.”

The piece, a theme with 22 variations, will have its world premiere today at 1, when members of the Philharmonic play it during the Promenade portion of their Young People’s Concert.

Once a week during an afterschool program, Deak invited the kids to make music any way they could – by humming, singing, tapping, or whistling. It was his job to transcribe it.

“I tell them not to be hung up on notes,” Deak said. “As long as they can give it to me the same way three times in a row, I know they’re really hearing something in their heads.

“But it’s their music. I didn’t add a single note.”

To help them know the instruments they were writing for, Deak had some fellow musicians stop by to play for the class. The result? A fairly pensive, minor-key theme with variations titled “The Family Parade,” “Anger in the Air” and others.

“It’s art by children,” said Deak, whose own kids Forrest and Selena are in the writing class, “but it’s not children’s art.”

Tickets to today’s concert at Avery Fisher Hall are priced from $6 to $24. For more information, call (212) 875-5030.