For years now we’ve reserved top billing on our holiday shopping list for kids we don’t even know. Last year, Jason, 6, got puzzles and a train. The year before, we bought Michelle and Neesha (sisters, 7 and 9) Old Navy puffy jackets and glitter pens. We signed the cards, “Love, Santa.” The kids? Well, they just knew they wrote to Santa — and he got the message. We received the letters through “Operation Santa Claus,” a program created 70 years ago by the New York post office. Every holiday season, letters addressed to the North Pole are distributed to anyone who wants to make someone’s Christmas wishes come true. Most of the notes (they get about 300,000 per season) come from underprivileged children. So come on, Santa’s helpers: Join the fun. Drop by the main branch of the post office, and select a letter or two. If you can’t pick one up, call and they’ll send you one. But don’t dally: These gifts have to arrive by December 25! (And don’t worry, the post office is taking extra special care with the mail this year. All Santa letters are being carefully sanitized.) Too bad we can’t get Rudolph to help carry your shopping bags. Operation Santa Claus letters are available at the main New York branch of the post office (421 Eighth Avenue, at 33rd Street; 212-967-8585) through December 22. Hours are Mon.-Wed. and Fri. 8 a.m.-4:30 p.m., Thurs. 8 a.m.-7 p.m., Sat. 9 a.m.-4 p.m.