Tunnel vision at the White House on Lt. Col. Oliver North's remarkable performance in the witness chair was reflected by counsel A. B. Culvahouse at the Wednesday morning staff meeting.

North's opening-day testimony, said Chief of Staff Howard Baker's close adviser, had something for everybody. Culvahouse meant that President Reagan was hurt when North said he assumed presidential approval of Iranian arms-sales funds for the contras but was helped when North said he had not discussed it with Reagan himself nor ever seen presidential authorization. Reagan's men grumbled over their morning coffee that The Washington Post and The New York Times made more of the former than the latter.

That missed the point of North's testimony, just as the White House has so often misunderstood the political significance of the Iran-contra affair. While presidential aides were morose that Reagan had not been fully exonerated by an inquisition they pretended not to watch, champions of the president's contra policy had their first good day in months.

In turning the tables on the committee, North did what the White House has never attempted since the scandal broke last November: put congressional opponents of contra aid on the defensive. For the first time, television viewers witnessed an articulate, impassioned defense of covert action in ''a dangerous world.''

Nobody who knows Ollie North expected retreat, particularly with blue-ribbon criminal lawyer Brendan Sullivan at his elbow. North's unexpected bonus was the choice of House counsel John Nields to open questioning. Wearing emotion on his sleeve, he lacked the courtroom presence of Senate counsel Arthur Liman, the experienced, ferocious litigator.

By delivering a rational explanation of what has looked like a government gone berserk, North has given the president a chance to regain the initiative. But that would require a White House breakout from tunnel vision. None seems in sight.

With Culvahouse the designated hearings-watcher, other aides were actually instructed not to watch Ollie on television. Sneak-peekers who closed their doors and reduced volume risked undermining the absurd impression that the president and his senior aides couldn't care less what North said.

While the nation was transfixed watching North make monkeys out of his interrogators without breaching good manners, the president was in Connecticut pursuing his feckless campaign for a constitutionally imposed ''supermajority'' on tax increases. In fact, the White House is not all that uninterested. On the narrow question of presidential culpability, with overtones of Watergate and impeachment, North was under avid inspection. The president himself watched on Thursday.

Hard-liners scattered throughout the administration attribute Reagan's ''rope-a-dope'' defensive posture to press spokesman Marlin Fitzwater, the designated Iran-contra voice. They would prefer a watered-down version of ex-communications director Patrick J. Buchanan's column in Newsweek.

Although Buchanan's assertion that the congressional Democratic Party ''wants the other side to win'' in Central America is unacceptable even for these Reaganauts, they know he is pointing in the proper direction -- a direction not on today's White House map.

North's testimony, dreaded at the White House for weeks, was cathartic for second-string Iran-contra victims who believed they were doing the president's bidding. One such prosecutorial target, career in ruins and financial security threatened by legal bills because he followed orders for a cause he believed in, told friends he felt revived. North's testimony did not address the special problems of this victim, but it reassured him he had not become an outcast fallen in an ignoble cause.

Herein lies the irony of the drama on Capitol Hill. Justification of Reagan's pro-contra policy comes not from the Great Communicator, bogged down in numbing, cross-country advocacy of budgetary reform. It comes from a Marine lieutenant colonel who faces criminal indictment and who, until this week, had lost even his allies on the right.