Nancy Reagan learned of her mother's death yesterday from President Reagan,who left the Oval Office at 3 p.m. to tell her personally.

"Later the president sat on the edge of the bed with her, and she was going through pictures of her mother, telling him, 'This is when she said this, this is when she did that,' " said Elaine Crispen, press secretary to the first lady, who only Thursday returned to the White House after surgery for breast cancer five days earlier.

"She's taking it very hard," said Crispen. "She and her mother were very, very close. Not a day went by that Mrs. Reagan didn't call her."

The first lady last saw Edith Luckett Davis, 91, on Aug. 13, on a trip to California. Crispen said she had planned to stop in Phoenix next month en route to the Reagans' Santa Barbara ranch for the Thanksgiving holiday.

Today, the Reagans fly to Phoenix, where Mrs. Reagan will stay for the remainder of the week. Reagan returns to Washington tonight, then goes back to Phoenix later in the week, the White House said.

Jim Duffy, the ABC executive who minutes earlier had delivered a report on PLUS (Project Literacy U.S.), felt a tug on his arm at the Labor Department Friday when the presentations were all over.

"I'm very concerned about one of your employes," said Ronald Reagan.

Duffy, caught off guard, ran through a mental checklist of ABC employes Reagan might know, including White House correspondent Sam Donaldson, but couldn't figure out who Reagan was talking about.

"Who's that, Mr. President?" he asked.

"My son," Reagan replied, meaning of course Ronald Prescott Reagan, a member of ABC-TV's "Good Morning America" cast, which had been filming in the Soviet Union for a couple of weeks.

"We can't get in touch with him," Reagan continued. "He's lost. He hasn't been heard from for a couple of days."

Duffy not only agreed that something had to be done but afterward he went straight to the phone and called New York. As one might expect, Ron Reagan wasn't really lost, just busy. You know how kids are.

To say nothing of dads.

If nothing else ever comes of U.S.-Soviet summitry, the British can always do a sequel to Granada Television International's new made-for-TV movie, "Breakthrough at Reykjavik," and call it "Breakdown in Moscow."

It isn't the first time Granada has dramatized and reconstructed a news event. Old hands at British cabinet crises and European summits, Granada officials were so impressed by the information the Soviets put out after Reykjavik that they dispatched a research team to get the other side of the story from U.S. sources.

After that, Granada, whose credits include "Brideshead Revisited," "The Jewel in the Crown" and "First Among Equals," hired playwright Ronald Harwood, who wrote "The Dresser," "Interpreters" and the screenplay for "One Day in the Life of Ivan Denisovich," and told him to tell the story in an hour. That he was able to may say as much about Reykjavik as it does about Harwood.

In any case, the results will be previewed here Nov. 3 at a special screening cohosted by Granada's chairman, David Plowright, and the British Embassy. In the audience are expected to be such real-life Reykjavik summiteers as Kenneth Adelman, director of the Arms Control and Disarmament Agency, and Richard Perle, former assistant secretary of defense. Afterward, they'll join a panel discussion on issues their movie selves (actors Ron Berglas and Garrick Hagon, respectively) dealt with onscreen and try to relate them to what happens next. Stephen Band, the embassy's politico-military affairs counselor, will moderate.

A horse of another color in U.S.-Soviet relations is the Russian thoroughbred that will be racing in the Washington D.C. International at Laurel Race Course Saturday. Credit for that goes to Armand Hammer, Occidental Petroleum's chairman and CEO, who asked last May if the Soviets would send an Arabian to the race.

Hammer, with Miami businessman Alec Courtelis, is a longtime importer of Arabians, including Russian stock, so when Laurel President Frank J. DeFrancis expressed interest in reinstating Soviet participation in the international race after a 25-year hiatus, Hammer passed the word.

"It was significant that Mikhail Gorbachev gave the go-ahead, because without his consent it would not have happened. As a result they've sent two of their finest stallions," Hammer said yesterday.

On the aborted summit, Hammer said he was "as surprised as anybody else" and thinks that something triggered the Soviets' "mistrust -- there's mistrust on both sides." He said he's due in Moscow next month when he hopes to see Gorbachev and "I hope I can do something."

Liz Carpenter says she clean forgot she was 67 when she agreed to be a media star and social butterfly. But today, 121 talk shows and dozens of Hollywood, Chicago and New York parties after the June 22 launching of her latest book, "Getting Better All the Time," she can't keep up with herself.

"If there's a copy of my book around that I haven't personally autographed, I want to see it," Carpenter said yesterday from Texas.

She'll have that chance on Sunday at the Texas State Society when she and author Larry L. King poise their pens for their transplanted Texas fans at a Tex-Mex brunch at the Hyatt Regency here. Starting at 6:30 p.m. on Monday at the National Archives Theater she'll talk about her book and the use she's made of presidential libraries scattered around the country in almost every region except one. Noted Carpenter, ever the pol-watcher: "We need a president from the Pacific Northwest. So how's {House Majority Leader Rep.} Tom Foley {D-Wash.}?"

White House Press Secretary Jim Brady's "thumbs up" comeback story of courage and hope is out now in the book of the same name, written by Mollie Dickenson and published by William Morrow and Co. Brady, who was wounded in the 1981 assassination attempt on President Reagan, and his wife Sarah begin a 2 1/2-week book promotion tour on Nov. 5, appearing first on "Donahue" and the following day on the "Today" show. Here in Washington, the Bradys and Dickenson will preside over a couple of "Thumbs Up" publication parties, one on Thursday night at the Four Seasons Hotel and another on Sunday at the Politics and Prose bookstore. And as one might expect, the list of invitees reads like a Who's Who of the Reagan administration and Washington media.