If "Animal House" didn't conclusively prove that grossness leads to grosses, then "Porky's" looks like it could settle the argument for good. The high school coming-of-age story--set in the South in the early 1950s--is by all reports the lewdest and crudest film to come along in a couple of years, and it was also the country's biggest moneymaker last weekend, pulling in over $7.6 million in three days. All this for a film that nearly died before it made it into nationwide release: Simon Productions, which made the film, had to substantially cut back its operations last fall, and in doing so they left "Porky's" dormant until they could form a partnership with Alan Landsburg Productions and Reeves Communications, Landsburg's parent firm. Even then, nobody was quite sure how to handle the rude little film--but test engagements in Colorado Springs, Colo., and Columbia, S.C., went over so well that 20th Century-Fox stepped in, made plans for a major release and went to work formulating several different marketing campaigns to make sure that the film attracted more than just the hormonally imbalanced high schoolers it depicts. Said one Fox staffer after seeing the weekend grosses, "I guess we're not gonna need all those complicated strategies, are we?"