Presidential speechwriter Peggy Noonan had wanted to do it but had forgotten to ask. When she found that President Reagan's speech at the John F. Kennedy Memorial Library fundraiser had been put on her schedule, she wrote a note to her boss, Bentley T. Elliott, thanking him very much.

"He never said anything, but he winked," Noonan, 34, said yesterday. "I think he probably thought, in an amused way, 'Well, here's an Irish Catholic with a liberal Democratic background . . .' "

And, indeed, Noonan, who describes herself as "your basic supply-side conservative -- I'm pretty conservative," was all those things growing up in a working class family devoted to the political philosophies of Franklin Delano Roosevelt and John Fitzgerald Kennedy. Kennedy was her special Lochinvar, a hero to many then but especially to an idealistic 13-year-old.

Later, she became convinced that the conservative movement was the way of the nation's future. But she remembers how Kennedy "gave us all the feeling of limitless possibilities, made politics seem like a marvelous calling. My whole family just loved him.".

After she was graduated from Fairleigh Dickinson University, and there was nothing she could do but write ("I couldn't even ride a bike"), she realized that "writing is easy when it's inspired by love and real affection."

So it sounded Monday night in President Reagan's moving and poetic tribute to Kennedy, a speech as representative of Reagan's feelings, according to Noonan, as of her own.

However Reagan may have castigated Kennedy in the past on issues, Monday's speech "very much reflects the president's point of view . . . about Kennedy the man," Noonan said. "He feels: 'How can you look back and not think he was a good fellow?' Which comes out when he says he didn't vote for him but that . . . 'when the battle's over and the ground is cooled, well, it's then you see the opposing general's valor.' "

Reagan may not have actually composed that exact combination of words any more than he did those for another Noonan speech -- the president's emotion-charged address to aging and maimed American veterans gathered at Pointe du Hoc, France, for the 40th anniversary of D-Day.

But they represent his sensitivities, and, his staff says, his interpretations of ideas and events. He becomes so involved in the evolution of his speeches, his speechwriters say, that the words become his more than theirs.

Political speechwriters never say they wrote a particular speech, only that they worked on it; colleagues say Noonan, who has worked for Reagan only since April 1984, is as sensitive to the president's pacing, phraseology and speech patterns as any in Elliott's shop.

Noonan said she and Reagan never actually met on the Kennedy speech but talked on the telephone "two or three times. I'd send him a draft, he'd send one back -- six times in all. I remember particularly that he had been very impressed by John and Caroline Kennedy, (and) by her (Caroline's) concern about history as an abstraction."

In working on the speech, Noonan said, it became apparent that Reagan not only liked Kennedy, but has a "profound feeling for him" and is inclined to get "a little rosy-eyed about him." He also appeared aware of the inspiration Kennedy had provided members of Reagan's White House staff.

"It is a matter of pride to me," Reagan said Monday night, "that so many men and women . . . inspired by his bracing vision and moved by his call to 'Ask not . . . ,' serve now in the White House . . . ."

Those staffers belong to a generation in high school and junior high at the time of Kennedy's death, young people for whom Kennedy had made politics seem like "a marvelous calling, a noble profession," said Noonan.

Former presidential assistant Richard G. Darman, an undergraduate at Harvard during the Kennedy years, once wrote Reagan in the White House about the Kennedy inspiration in a letter later released to the press. Even today, Noonan said, speechwriter Anthony R. Dolan has a large picture of the late Robert F. Kennedy in his office.

Noonan's calling to the "noble profession" came from Ben Elliott during the 1984 New Hampshire primaries. Elliott had been telephoning around asking about candidates for a speechwriting job and Kevin Lynch at the National Review told him about Noonan, a conservative as well as a writer.

After nine years as a television and radio producer and writer, doing scripts for Dan Rather, special reports for CBS Television in New York and news reports and editorials for a CBS-owned station in Boston, here was her chance at politics with a capital P.

"I said I wanted to think about it for a few days, and the day after the primary, as I sat and pondered, I looked across the room where Bill Moyers was working on his script. I grabbed him and said, 'I got to talk to you, let me buy you a beer,' " Noonan said.

As she told him about the offer, Moyers leaned forward and asked: "In 200 years of American history, how many people have worked for a president? Five thousand?"

Noonan said: "I'm taking the job." And Moyers said, "Of course you're taking the job."

Later, when she told her mother, the reaction wasn't unexpected:

"She said, 'You know, your grandfather always said stick with the Democrats, they're the party of the working class.' I said, 'If Grandfather were here today, he'd be a conservative.' And she said, 'You're probably right.' "