IF YOU WANT to know what Nancy Reagan wore to the tea dance where she made her 1939 Chicago debut, then read Laurence Leamer's Make-Believe: The Story of Nancy and Ronald Reagan. If you want a sanitized, almost ludicrous version of the 1976 and 1980 Reagan presidential campaigns by a loyal courtier, then try Peter Hannaford's The Reagans: A Political Portrait.

It's just 21/2 years into the Reagan administration, but here come the books on the First Couple America loves to gossip about. These two are so disappointing that you have to wonder if the "Reagan Era," as Hannaford calls it, hasn't run dry of its last available fact. Neither book offers anything particularly new.

Leamer, a Washington free-lance journalist and author, has essentially compiled newspaper and magazine articles of the past few years into an entertaining collection of anecdotes. Leamer says 400 people were interviewed for the book, suggesting that it might have been the definitive tattletale. But mostly he repeats the same old stories about the White House china, Nancy's Rodeo Drive friends, and the sad little girl who grew up in Bethesda.

There are a few surprises. We learn that Ronald Reagan, in between Nancy and his first wife, Jane Wyman, was an unhappy bachelor-about-Hollywood who once told Joe Santley, a public relations man, that "I woke up one morning and I couldn't remember the name of the gal I was in bed with. I said, 'Hey, I gotta get a grip here.' "

We learn that Nancy, as a struggling actress, used to filch dinner rolls at the Stork Club in New York, stuffing them into her evening bag with such regularity that one evening owner Sherman Billingsley sent over a pound of butter with the note: "I thought you might enjoy some butter on my rolls." We also read that Nancy, as a contract player for Metro-Goldwyn-Mayer, was "dating" Benny Thau, an M-G-M vice president. In a peculiar paragraph attributed only to "Barbara," Thau's "pretty teen-age receptionist," we're told that Barbara "had orders that on Saturday morning Nancy was to be sent directly into Benny Thau's suite. Barbara nodded to Miss Davis as she walked into the vice-president's office; nodded again when she left later."

And we hear about the unique generosity of the Reagans' California friends, particularly when then Governor Ronald Reagan and his wife were renting a house in Sacramento. Leamer writes that 17 of the friends bought the house for $150,000, then rented it back to the Reagans for $1,250 a month.

Leamer's theme is that the Reagans grew up in hard- knock worlds where they had to make-believe, married in Hollywood where the town made-believe for them, and now continue to create their own "make-believe" world in Washington. He writes with few judgments, his one-fact-after-another pattern broken only by occasional cattiness (playing Carmen Miranda at Smith College, the 5-foot, 4-inch, 130-pound Nancy was "just plump enough to look like a luscious piece of fruit herself.") Too often, he strains for effect. Former White House political director Lyn Nofziger has an ego "as big as a redwood tree." Ronald Reagan fit the role of GE Theater host "like a light bulb fit a socket," and Nancy "was holding her son up to daily scrutiny, like a wineglass smudged with fingerprints." In another annoying habit, he refers to Reagan as "Ronnie" throughout all 395 pages. When "Ronnie" takes the oath of office and "Ronnie" goes to the European economic summit, it begins to sound like the bachelor-of-the-month in a Cosmopolitan magazine article.

The important question about Leamer's book is whether it will change the public's perception of the Reagan presidency. Probably not, because people have already made up their minds. For administration critics, the book will simply confirm all the things they suspect, particularly about Nancy's problems with her children, her love of the sparkly set, and her ambitions for herself and her husband all here in the most comprehensive catalogue to date. For Reagan fans, it will be another blast of cheap shots by a journalist.

Peter Hannaford's The Reagans: A Political Portrait is really about a make-believe world--the author's. Hannaford, a former Reagan speechwriter and adviser who is now a public relations man, describes the 1976 and 1980 Reagan presidential campaigns, which were filled with infighting, mistakes and touches of brilliance, as pleasantly distracting travelogues. The considerable political egos are motivated by nothing less than patriotism; in Hannaford's world, no one gets mad and no one yells. He also has one of the more homogenized versions of the rupture created in the 1980 campaign by manager John Sears. Describing a well-known and violent shouting match between Sears and Reagan, Hannaford merely writes that "tensions spilled over." He doesn't elaborate, or mention, as has been widely reported-- including in Leamer's book--that Reagan got so furious at Sears he almost hit him.

But Hannaford set out to write an official history. He is capable of composing this first sentence in the book without a trace of irony or embarrassment: "We embraced briefly; then Nancy Reagan looked at me and, with a half-smile, said softly, 'Did you think it would ever really happen?' " It was November 4, 1980. "I could not find the right answer. I was numb, but I did manage to say, 'What a glorious evening!' "

Moved as we are by this, Hannaford could at least have written a thoughtful account that tells us something new about the man he is said to be so close to. (In a description thattmight startle some White House advisers, the author is touted on the book flap as "the man 'most inside' during Ronald Reagan's historic campaign for the presidency.")

Here is what passes for insight: "If, as the day progressed, (Reagan) tired of answering the same questions or making the same points about issues, he did not show it. His ready smile and good color made him seem all the more energetic and youthful in the crisp February air." And when it's all over, here is his observation on the modern political process: "What a mixture of influences a campaign is; the constantly changing interplays of personalities, ideals, sometimes conflicting motivations."

What Hannaford lacks in freshness he makes up for in speeches, many of them written by himself, that he quotes at length in the text. Reagan's speech accepting the 1980 Republican nomination in Detroit takes up a full 41/2 pages. It is not compelling reading, although maybe it helps if you were there.

Hannaford, who was, says he felt tears stream down his face.