Geraldine A. Ferraro's senior aides reacted with a blend of skepticism and humor today to reports that their counterparts in Walter F. Mondale's camp believe that President Reagan has an insurmountable lead.

John Sasso, Ferraro's campaign manager, said The Boston Globe report today was incorrect in asserting that James A. Johnson, Mondale's campaign manager, believed that Reagan's margin in the polls could not be overcome.

Those denials notwithstanding, other Ferraro aides could not resist poking fun at Mondale's staff after hearing of the Globe report.

"We're going to drag them kicking and screaming across the finish line to victory whether they want it or not," said press secretary Francis O'Brien.

O'Brien spent part of this morning outlining plans for what he called "a guerrilla campaign" for victory on Nov. 6. The strategy includes having the candidate, staff and press corps take to "the hills" to hunt electoral votes. O'Brien, noted for his tweedy wardrobe as well as his wit, said that before the guerrilla war begins, "we need some new outfits."

Steven Engelberg, the campaign issues director, announced to the press corps, "My first assignment is to kill Francis before he does any more damage."

There seems to be a loose and free-spirited mood within the Ferraro campaign despite portents of impending defeat.

The candidate, who admitted to being "testy" earlier in the week, showed symptoms of that attitude while campaigning in Oregon today, quipping frequently to the crowds and exhibiting a self-deprecating humor, as when she said, "I'm trying to learn not to say 'lemme.' I've got to learn to say 'let me.' "

"You know, I can read the polls, and I've heard reporters' questions when they say, 'How can you win this race?' " she told a crowd of4,000 on the University of Oregon campus. "Well, let me tell you . . . . I believe that you, the people here today, care about peace, you care about arms control, you care about the environment, you care about personal freedom. I know that because you care, on Nov. 6 . . . , by the millions, you're going to turn out and vote for a better future."

During a citizens' forum in Medford, she said, "The thing that gets me is people say, 'President Reagan is a nice man.' And he may very well be. Like him, but don't vote for him."

She warned that Reagan has escalated the arms race with the Soviets. "Every day we have not negotiated a treaty, we are building between us, a conservative estimate, five to six more warheads. Since this administration came into office, 2,500 more warheads are pointed at our cities because of no ratification of SALT II."

Ferraro appeared to be blaming Reagan for the failure to ratify the second strategic arms limitation treaty. It was withdrawn from the Senate by President Carter after the Soviet invasion of Afghanistan. The United States and the Soviet Union have said they will abide by the limits negotiated in the treaty even though it has not been ratified.