Though known as a workers’ holiday honoring the right to work less, May Day originated as a pagan festival celebrating the first spring planting (and free sex). So what better day to rally to free the herb? Yippie Dana Beal and his crew of hardcore marijuana crusaders began hosting this annual pot parade in 1973. It’s since mushroomed into a global happening in more than 160 cities. Don’t expect folks to be tossing out bags of free joints as in the heady days of yore; organizers warn that anyone lighting up may be arrested, as were nine last year and some 300 in 2000. “It’s a protest, not a pot fest,” says Beal. And thanks to a Giuliani-initiated crackdown, pot revelers can no longer gather in Washington Square. But there’s still plenty to get fired up about, not least the feds’ ongoing assault on medical-marijuana users. The march begins at 1 p.m. on the corner of Houston and Broadway and proceeds down Broadway to Battery Park for a rally featuring Queens Assemblyman Jeffrion Aubry, Rockefeller drug laws foe Randy Credico, and Shattered Lives author Mikki Norris, plus music by ex-Misfit Bobby Steele, the David Nelson Band, Stir Fried, and special guests. K-Rock’s Liquid Todd and Influx from Brazil will be spinning at the north end of the park for those who just want to chill.