Robert E. Dolan, the chairman of Young Americans for Freedom who appeared with President Reagan at last week's Conservative Political Action Conference, suddenly resigned from the organization last Sunday, before his term was complete, YAF officials said.

Terrell Cannon, a Lincoln, Neb., attorney, who was elected chairman by the YAF board, said the resignation came for several reasons, including "philosophical differences" with the board and questions about Dolan's outside political and business activities.

Cannon refused to be specific, but said Dolan's standing in the organization was "hurt" because the directors were not aware of his involvement in other "private political action committees." Cannon also said there were "attacks" on Dolan concerning his handling of YAF business, but would not provide details.

Cannon said he had requested a "comprehensive report" on YAF's financial and membership situation in the wake of the resignation. "I have asked our people to go over everything," he said, adding that he is "not proceeding with the assumption that Mr. Dolan did anything wrong."

"We've got the situation rectified, solved, controlled," he said.

Republican political sources said the resignation marked another in a wave of turmoil and infighting that has racked the conservative youth organization for more than a decade.

Lewis Doherty, a spokesman for YAF, said Dolan left for "personal reasons." He refused to say what led to the resignation but said the group had no outstanding legal complaints against Dolan.

Dolan could not be reached for comment. His two-year term as chairman was to expire this summer, Doherty said.

Dolan also was elected last weekend to the board of the American Conservative Union, which cosponsors the conference with YAF, Human Events and the National Review. David A. Keene, chairman of ACU, said Dolan was elected last weekend to a seat on the ACU board that is reserved for the YAF chairman, and he assumed Dolan also would be quitting the ACU board.