His aides want everything to be as easy as possible for President Reagan as he recovers from his operation, but there are some decisions only the First Patient can make.

Like what he reads. So far, the president's choices have been Louis L'Amour's bestselling "Jubal Sackett" and a new biography, "Return to These Hills: The Vermont Years of Calvin Coolidge," which has yet to make the best-seller lists, and "A Treasury of Will Rogers."

"He's always liked to read," said Peter Roussel of the White House press office.

And he's always liked Calvin Coolidge.

"He wanted a portrait of my father in the Cabinet Room," said John Coolidge, who wrote the forward to the book, "so he has one."

Was he gratified by the president's choice of reading material?

"Yes," said Coolidge, "of course," with a restraint suggesting taciturnity may be hereditary.

Outside the immediate family, the response was somewhat more energetic. "Great excitement!" said a laughing Fred Lieberman, a coauthor of the Coolidge book. "Fame! NBC was desperate to get the book for the news. There was quite a hoo-ha getting a copy of the book to a plane to get it to Boston to beam it down. They got it on during the last minute of Tom Brokaw. It was great fun.

"I think Coolidge embodies all the virtues important to the president -- thrift, honesty, hard work, all that. All the so-called Vermont virtues, which is what our book is about."

John Coolidge, Lieberman and coauthors Jane and Will Curtis all signed a copy and sent it off to Reagan before his hospitalization.

"We thought that we might get a nice letter from him," said Leiberman.

Instead, Fame! Excitement!

"Jubal Sackett," the 18th book in L'Amour's Sackett saga, is about a 17th-century explorer in Tennessee and the Carolinas. It is not, says Bantam Book's Stuart Applebaum, "strictly a western." This did not seem to bother the president, who already owns a leather-bound copy of L'Amour's "Hondo," presented by L'Amour.

L'Amour, who has received the Medal of Freedom and a Special Congressional Gold Medal and who has 160 million copies of his books on bedside tables around the world, was even less voluble than John Coolidge about making the president's reading list.

"He felt it would be exploitative to talk about it," said Applebaum, vice president at Bantam, which publishes all of L'Amour's books. "He has no interest in doing four-alarm press interviews. We all know people who would turn this into a personal publicity feat. He says he feels very uncomfortable taking advantage of it. That's the kind of person he is."

Now, all this doesn't mean Applebaum had to be as restrained. "When Reagan reads it," he said, "because he is who he is and there's so much interest in what he's doing -- it creates a worldwide interest in L'Amour."

The presidential doctors have yet to prescribe novels or biographies, but according to the 1983 Consumer Research Study on Reading and Book Purchases conducted by the Book Industry Study Group Inc., all the reading may be therapeutic.

"Senior book readers are more active than non-book readers or non-readers," found the study, which defined "senior" as over-60. "Senior book readers are more likely to socialize, attend club meetings, knit or crochet, play cards or keep physically fit than non-book readers or non-readers."

The study did not address the question of whether reading about Calvin Coolidge offers any added benefit.