Ah, soon the pitter-patter of little feet - lots of them - might be heard at the White House. Millie, President-elect George Bush's springer spaniel, has spent the past two weeks at a farm in Kentucky, where she was bred with Tug, a springer spaniel owned by Will and Sarah Farish. "We believe she's pregnant, but we don't know that for a fact," Farish said Monday. Farish said they would know in about three weeks if the 2-year-old dog is pregnant. If she is, she likely would give birth in March. The Farishes gave Millie to Bush and his wife, Barbara, about a year ago. Farish said he telephoned Mrs. Bush on Friday and told her everything had gone fine. "She's very close to Millie," he said.