ON THE GUMP: As Forrest Gump, Tom Hanks finds himself in the company of such U.S. Presidents as John F. Kennedy and Lyndon Johnson — and it's not that far-fetched. In real life, the Oscar-winning Hanks has shaken hands with his share of Commanders in Chief. ''I met George Bush at a big kind of dinner and said 'Howdy-do,''' says Hanks. ''Then I met Bill Clinton during a tour of the White House.'' But Hanks' most presidential moment came at yet another meeting with Clinton. ''After a screening of Philadelphia, I was invited to spend the night (at the White House). We stayed in the Queen's Bedroom, and I must say, it's the best bed-and-breakfast in the United States of America.''