President Jimmy Carter, in one of his last presidential acts, conferred the Medal of Freedom yesterday on 15 citizens in ceremonies at the White House.

The medal was thought up by Harry Truman, as the nation's highest decoration for civilians.

When former United Nations ambassador Andrew Young got his yesterday, the president spoke of his outstanding humility.

As he said, to begin with, there are tens of thousands of Americans who have made substantial contributions zub zub zub to the national security and honor and luster and the fact that 15 were named to this honor yesterday was no derogation to those who were not named.

He mopped his face once, being president, as the 150 guests sat proper and unmopped in a room blazing with television lights that brought the temperature and the general boombah to about 92 degrees.

Not surprisingly, some of the nation's most distinquished men and women turned out to be government employes, such as Harold Brown, secretary of defense; Zbigniew Brzezinski, the president's adviser for national security; Gerard C. Smith, former director of the arms control agency; Robert Strauss, Democratic wheelhorse and former special trade representative; and Andy Young.

Warren Christopher, who the president said had impressed him more than any other government servant, and who keeps coming and going about the Iranian hostages, was honored (the medal accepted by his wife) and so was Esther Peterson, consumer affairs duchess who alone got a presidential kiss, possibly because she trembled as if she had never been before an audience. Secretary of State Edmund Muskie bowed to have his medal hung on his neck along with the others.

Roger Baldwin, founder of the American Civil Liberties Union, now ill, received his medal from a presidential agent at his hospital bed. With him, a slightly different order of excellence was honored. Baldwin was never paid, or sworn, to do anything.

Walter Cronkite, CBS newscaster, was honored for many years of delivering the TV news which, the president said, was done in a way to keep people from going berserk or falling into panic. A notable service, some thought.

Dr. Karl Menninger, psychiatrist, did not show up for his medal -- and one detected just a trifle of presidential annoyance here -- but a "less valuable nephew," Roy Menninger, showed up to accept the honor.

The ceremonies lasted an hour or so, but since the president stood throughout, nobody could say they lasted too long.

Kirk Douglas, actor; Federal Judge Elbert Tuttle (who bore some of the brunt of enforcing civil rights in Georgia) and the late Chief Justice Earl Warren were all honored. The chief justice's widow accepted the medal. She was dressed in black with a long string of pearl beads and, unlike most recipients, graciously acknowledged the long applause that greeted her appearance.

Margaret McNamara was announced, and was wheeled up before the president in her chair by the handsome military aides present. The room went wild with applause. Here is what Margaret McNamara did for the nation:

She once ran into a bunch of kids who had never had a book of their very own. This set off her fuse. She by God saw to it they got some books they never had to return but could keep forever. She has spent years pushing a program in which kids get books they can keep forever.

The president, in perhaps the most moving remarks of the day, said that what the country is really about is those good things. A private citizen -- for this woman had no official responsibility -- can get off his or her duff and do something. Not that the president put it so bluntly, but that's what all the applause was about. She nodded in her wheelchair to the audience, looking a few shades too modest, as if to say "Look, this wasn't my idea," and probably because she never expected any official honor -- as virtuous men expect none for mere virtue -- she was the sensation of the afternoon.

Her husband, Robert McNamara, former cabinet member, did not stay for the little reception that followed, but was busy at the front door of the White House opening glass doors, seeing the car was ready for his wife, and generally seeing to it she was made comfortable. As well (with such a wife) he might.