Today is the day his many fans finally get to give John Jackson a birthday party.

If you chance past the corner of 17th and C streets NW at about 4:45 p.m., you'll see a bevy of vans. Normally, at that hour, they're pooling federal workers out to the suburbs. But this afternoon, they'll be parked by the curb, and the occupants will be on the sidewalk, downing cake and champagne and declaring at the tops of their lungs that Jackson is a jolly good fellow.

Jackson is known to the van poolers as the Mayor of 17th Street. According to Jerry Jones, who passes Jackson every weekday on his way home to "beautiful Bowie," the Mayor always stands at 17th and C and always has "a friendly wave and a smile . . . . It's one of the highlights of our homeward journey."

Jackson was 75 years old on Dec. 22. But because he spends the winter somewhere warmer than Beltwayland, his fans couldn't catch up with him on the big day. So today, they're celebrating John's 75 1/2th birthday. All who have ever been on the receiving end of a Jacksonian wave are invited.