Thanksgiving wouldn’t be Thanksgiving without turkey and pumpkin pie. But it’s looking like this year, some households are going to have to do without the emblematic holiday dessert. This year pumpkin crops suffered from too much rain, which led to a shortage in the amount of pumpkin harvested. Roz O’Hearn, a spokeswoman for Libby’s, which produces almost all the canned pumpkin in the U.S., said that what’s on supermarket shelves right now is probably all that will be available through the holidays. “We know at this point the  harvest is going to be smaller than anticipated,’’ she said. “Does that mean it’s going to be increasingly difficult to find in stores? Yep, that’s probably likely.’’ Libby’s has been picking and processing its 2009 pumpkin crops as quickly as possible in an attempt to avert the crisis, but it’s unlikely that the small harvest will be able to meet the needs of American holiday cooks. “Most likely, we’re going to see our inventory dwindling soon,’’ said O’Hearn.