YESTERDAY Lt. Col. Oliver L. North acknowledged that at one time or another he had told a ''bold-faced lie'' to the Iranians, helped ''fix'' former CIA director William Casey's testimony to Congress, taken a role in preparing a false chronology in the White House, passed misleading information to President Reagan, misled the CIA and told a false story to Gen. Richard Secord. He also insisted he was a truthful man, doing presidentially authorized service, whose intent was never to deceive the American people but to keep American adversaries in the dark by protecting covert operations. Pressed at one point, he flashed a bit of temper, telling the assembled members of Congress it was a good thing others had cared more for the Nicaraguan resistance ''than this body here.''

Investigators have several days left in which they will try to augment the public record with information drawn from the highly articulate but -- when it comes to hard facts -- parsimonious Marine officer. Already it is evident, however, that the world of Oliver North is very different from the world in which so many other Americans reside. The world of Oliver North is one in which official missions take precedence, secrecy is the normal mode, shredders are a routine office machine and there is no room for doubts or constitutional scruples of any observable sort. It is a world in which the line between official and personal purposes was so blurred that Oliver North could refer to ''my private U. S. operation.''

This is the man who flourished in Ronald Reagan's White House. As much as anyone else there, he had the commitment and resourcefulness and -- with his military background -- the special skills to step up to the hard cases, the ones where the Cabinet or the bureaucracy or the legislature or the public were putting obstacles in the way of some of the president's favorite foreign policy designs. It evidently did not occur to him that there might be reasons of public policy, not to speak of constitutional considerations, why someone acting in the name of the commander in chief could not simply do what the mission required.

Now he is being called to account in a demanding public forum which is strange to him and whose inquiries he resists. The first day of his testimony was revealing.