The two candidates have packed their schedules with events for Monday in efforts to drum up last-minute support.
The former first lady told the Philadelphia Inquirer
newspaper that the Illinois senator was getting "desperate" and carrying out a negative campaign against her as the poll drew closer.
"I think he's doing what candidates do when they get desperate at the end of an election," Clinton said.
"He has spent all this time crossing Pennsylvania talking about how he runs a positive campaign, except when he gets pressed, and he starts throwing ... the 'kitchen sink' at me."
The two rivals had clashed over the weekend on health care and Clinton hit out at Obama after he said John McCain would make a better president than George Bush.
However, in an interview with a Pittsburgh radio station, Obama said he would do well.
"I am not predicting a win. I am predicting it is going to be close and we are going to do a lot better than people expect," he told KDKA. Delegate race
The Illinois senator is hoping for a landslide in the Philadelphia area, with its high numbers of African-American, young and more affluent voters, to counter Clinton's appeal in poorer, more conservative western parts of the state.
On Monday, the rivals both headed to Scranton, a tough town built on steel and railroads, where Clinton's grandfather once worked in a lace mill.
Clinton was due to host several rallies with her husband, former president Bill Clinton.
After a 15-month race, neither Democrat is expected to reach the tally of 2,025 nominating delegates to claim the nomination outright.
Obama now leads by 166 pledged delegates, 1,417 to 1,251, and leads overall by 142 delegates, 1,652 to 1,510, according to a count by MSNBC.
Clinton leads among the so-called superdelegates, 259 to 235, MSNBC said.
Clinton needs to convince nearly 800 superdelegates - senior Democrat officials who vote at August's party nominating convention - that it would be too risky to pick the inexperienced Obama to fight McCain in November.