On a day that President Reagan had intended to spend promoting his tax-overhaul plan, the president instead found himself in the middle of a self-created controversy involving the hijackers of the Italian cruise ship and the Palestine Liberation Organization, which the United States does not recognize.

In a planeside news conference at O'Hare International Airport here, Reagan said it would be "all right" for the four hijackers of the Achille Lauro cruise ship to be tried by the PLO if its leader, Yasser Arafat, has "kind of a national court set up, like a nation that they can bring them to justice."

The remark caused consternation among Reagan aides, who immediately realized that this would be tantamount to recognizing the PLO, which the United States considers a terrorist organization rather than a legitimate government.

When reporters alighted from a helicopter at the next stop, national security affairs adviser Robert C. McFarlane told them that the president "meant that he wants the PLO to turn these hijackers over to competent authority for trial."

A few minutes later and within an hour of his first comments, Reagan held another question-and-answer session and withdrew his remarks about the PLO trying the hijackers.

"I really believe that the PLO, if the hijackers are in their custody, should turn them over to a sovereign state that would have jurisdiction and could prosecute them as the murderers they are," Reagan said.

The president's position was complicated, officials said, because he did not know for certain whether the pirates had been released to the PLO or were still in Egypt.

White House spokesman Larry Speakes and McFarlane said that Reagan had received "conflicting reports" on the whereabouts of the hijackers.

Speaking to reporters in the employes cafeteria of the Kitchens of Sara Lee, Reagan said "apparently there's a little confusion, and maybe I'm responsible." The president said he had "not meant to imply" that the PLO should try the hijackers.