President Reagan will present author Louis L'Amour with a Special Congressional Gold Medal at a White House ceremony today. L'Amour, who has written 87 books about the American West, will be the first novelist to receive the award, which has been given to 79 individuals including Thomas Edison, Charles Lindbergh, Jonas Salk and John Wayne since it first was given to George Washington. Robert Frost has been the only other literary figure to receive the medal, which must be approved by both houses of Congress and signed into law by the president.

"There was just this spontaneous outpouring of support," L'Amour said in a recent telephone interview. "People from all over the country wrote to their congressmen about it. There was one lady down in Georgia who loved the books, so she sat down in her post office and got other people who read the books to sign a petition to send to their representative."

L'Amour said Commerce Secretary Malcolm Baldrige was one of his strongest supporters. He said Baldrige told him he had "read each of my books three times."

Jack Evans, a retired newspaper editor in L'Amour's birthplace, Jamestown, N.D., first approached Congress with the idea of honoring L'Amour four years ago.

"I wrote over 3,000 personal letters--personal, not Xeroxed," Evans said. "And I put out a so-called newsletter every two or three months saying what his new books were. There were fans from all over the country. There's a little old lady from Upstate New York, 92 years old, and that poor woman wrote personal letters longhand and I sent her postage money out of my own pocket.

"His books are read by truckers, everyone, and quite a few senators and congressmen. It's very easy to get people started--they read one book and get hooked on them. Men and women read them. If you want to read something that's about a woman, there's 'Conagher'--that has the cutest romance in it. There's a woman who's lonely and she writes love notes on the tumbleweeds. My favorite is 'Sitka.' It's about Sitka, Alaska. I was born up there. That's a real, rip-roaring good novel."

L'Amour said he thought an increased national interest in America's past contributed to the interest in honoring him.

"A few years ago there was all that fuss about 'Roots,' " L'Amour said. "Alex Haley is a very good author, but I think his book was a manifestation of something that was happening all across the country.

"I think that one of the reasons for my success is that America has reached a plateau in its history," he said. "Now we're stopping to look around and see where we've been."