JOHNSTOWN, Pa.  Senator Barack Obama had a few words of advice Saturday for his rival, Senator Hillary Rodham Clinton: Do not drop out on my account.

“My attitude is that Senator Clinton can run as long as she wants,” Mr. Obama, of Illinois, said at a news conference in a high school gymnasium here. “Her name is on the ballot. She is a fierce and formidable opponent, and she obviously believes she would make the best nominee and the best president.”

A few prominent Obama supporters have recently suggested that the time has come for Mrs. Clinton, of New York, to consider withdrawing from the race for the Democratic presidential nomination. Senator Patrick J. Leahy of Vermont, for one, said last week that Mrs. Clinton could not win the race and that her attacks on Mr. Obama were hurting “more than anything that John McCain has said.”

Mrs. Clinton’s forces have mounted a vigorous counterattack, saying she trails by a fairly narrow margin in the overall popular vote and in the delegate count. She has suggested to two allies that party leaders are trying to bully her.