A majority of Americans polled since Lt. Col. Oliver L. North began his testimony to Congress last week has formed a picture of the Iran-contra affair as a systematic policy run by a misguided but well-meaning Marine with the knowledge and approval of top administration officials, including President Reagan.

Polls released yesterday by Time magazine and Newsweek show that most respondents believe that Reagan has not told the truth in denying knowledge of the diversion of profits from U.S.-Iran arms sales to aid the Nicaraguan rebels.

With a New York Times/CBS News Poll published Saturday, the surveys reflect public sympathy for North, who was seen as a patriot by large numbers of respondents, and widespread skepticism toward an administration that originally attempted to focus blame for its most damaging scandal on North.

The polls were conducted Thursday and Friday as North, the fired National Security Council aide, drew key administration officials into the affair during four days of televised hearings before the congressional Iran-contra committees.

An overwhelming majority of those surveyed by the news organizations said they believed that North received authorization from his superiors for all his activities. More than two-thirds of 658 adults in the New York Times/CBS News Poll said that North had acted "with the knowledge and approval" of the president.

In the Time poll of 612 adults, 58 percent agreed that Reagan "knew money was being diverted" from the Iran arms sales to the Nicaraguan contras. Only 21 percent said they believed the president "has told the American people everything he knows" about the matter.

Sixty-one percent of the 620 adults interviewed for Newsweek said that by the time the investigations end, Reagan will "turn out to be more involved than he has said in the Iran-contra affair."

North's credibility compared favorably with the president's in the Times/CBS poll, with 62 percent saying the Marine was telling the truth in his congressional testimony. Fifty-six percent said they thought Reagan was "lying" in denying knowledge of funds diverted to contras.

Only 19 percent those interviewed for Newsweek said North was telling the whole truth at the hearings, with 53 agreeing that he was withholding information to "protect others" and 15 percent to "protect himself."

The polls reveal conflicting public perceptions of North, the flamboyant soldier who broke months of silence to testify last week.

Of Time's respondents, 77 percent agreed to the description of North as "a scapegoat for higher-ups" and 67 percent as a "true patriot." But only 29 percent viewed him as a national hero, 37 percent as "someone we need in government" and 26 percent as "someone I would want to marry my daughter."

While only 22 percent said they believe that his role in diverting Iran arms sale profits to the contras was legal, 69 percent said he should not be jailed.

The Newsweek poll found 65 percent agreeing that North was well-meaning but "did things that were illegal," 70 percent disagreeing that he should be indicted and tried on criminal charges and 55 percent disagreeing that he acted for personal gain or profit.

North's congressional appearance has clearly captivated public attention, according to the polls, with 71 percent of those interviewed for the Times/CBS poll saying they had listened to or watched at least part of the hearings.

Also, there were public concerns expressed about the fairness of Democratic-led hearings. Most of those interviewed for Time said the proceedings were motivated more by politics than by the evidence, and 48 percent of Newseek's respondents said the panel was harassing North.