President Reagan's doctors described his recovery from surgery in rosy terms, but the president's long-term prognosis will not be certain until doctors release the results of tests to determine whether the tumor they removed was malignant.

Those results were expected to be released today, according to White House spokesman Larry Speakes.

Tumors of the type and size found in Reagan's colon, villous adenomas measuring two inches across, have proved in the past to be already malignant in more than 50 percent of cases. Even if malignancy is confirmed, the president's doctors say the surgery already done may be "curative."

A small sample of the tumor, discovered in a diagnostic procedure last Friday, was removed at that time for analysis, but doctors have released only a "preliminary" report that it appeared to contain no cancer cells. No final report has been issued.

Today's results will be from a more complete study of the tumor and surrounding tissues removed in the operation.

According to Speakes, Reagan spent a peaceful night, interrupted only by attendants checking vital signs that remained "rock stable."

Dr. Dale Oller, who headed the surgical team, even invented what appeared to be a pseudostatistic to describe Reagan's condition. As quoted by Speakes, Oller said, "The president is on a post-operative course that surpasses, by 99.9 percent, all patients who undergo this type of surgery. That includes all patients, much less one who is 74 years old. So far, it is a spectacular post-operative course."

Speakes said Reagan has required no pain medication since Saturday, just after the operation.

But, Speakes noted, the president's temperature was slightly above normal for a nonsurgical patient, "Up just a notch but well under a hundred." Speakes said he did not know the exact temperature.

Slightly raised temperatures are common during the day after surgery, and doctors generally do not consider them anything to worry about. Post-surgical infection, which can raise body temperature, is not usually evident until several days after an operation. Speakes said doctors had found no sign of infection in Reagan.

Nancy Reagan arrived from the White House to visit the president about 10 a.m., spent the morning with him and had lunch in his room. Reagan's lunch, if it can be called that, was supplied by an intravenous tube that delivers nutrients to his bloodstream. It will probably be two or three days before Reagan can take liquids by mouth.

Speakes said Mrs. Reagan left her husband alone for much of the afternoon, thinking he would take a nap. Instead, the president read a new novel, "Jubal Sackett," by Louis L'Amour, one of Reagan's favorite authors.

"The president's frame of mind is excellent," Speakes said. "He's always chomping at the bit to do a little bit more than the doctors want him to do. All in all, it's been a first-rate, first day after surgery."

Results are to be available this afternoon from the malignancy test that has been under way since just after the tumor was removed Saturday afternoon. If the tumor contains malignant cells, there is a possibility that some had already escaped and been carried through the bloodstream to other parts of Reagan's body, where they can seed new tumors.

Although doctors saw no immediate signs of tumors elsewhere, when they examined Reagan's internal organs during the operation, the early stages of cancer origin and spread are microscopic. They can be found only by removing suspected cancerous tissues and preparing them so that the cancer cells can be distinguished under a microscope.

The preparations begin with soaking the tissues in a preservative solution called formalin for several hours. Then, the tissue specimens would be embedded in hot wax that hardens, so that they can be sliced thinly without tearing.

The paper-thin slices must be treated with chemical stains that make specific features stand out under a microscope. Then the procedure relies on experienced eyes. Pathologists must examine slices from all the removed tissues and search for cells with the characteristic features of a cancer cell.

Asked whether the president was prepared to face the prospect of an unfavorable lab report, Speakes said, "The president is pretty much of an optimist. When you get to know the man, you know that he can handle anything that comes down the pike."

Although Reagan's apparently speedy recovery continues to impress his doctors, other specialists note that it is not a debilitating type of intestinal surgery. Removal of the left colon, for example, rather than the right, as in Reagan's case, usually forces patients into a more difficult recovery period.

After an operation like Reagan's, most patients remain attached to several tubes for the first day or two -- an intravenous feeding tube for fluids and antibiotics, a nasogastric tube that draws air and fluid from the stomach and a catheter to keep the bladder empty.

By the second or third day after surgery, according to Donald A. O'Kieffe, a Washington specialist in colon cancer, most patients are encouraged to walk around in the hall.

O'Kieffe said the nasogastric tube is typically removed on about the third day, and, if all goes well, Reagan will probably begin receiving clear liquids on the fourth or fifth day. If he has no trouble digesting these, he will be allowed increasingly challenging foods until, by the time he is discharged, perhaps early next week, he should be on a nearly normal diet.

O'Kieffe said Reagan's doctors will probably tell him to avoid climbing stairs or exercising vigorously for several weeks. "A month after surgery," he said, "most people are fairly functional."

Asked whether the president is likely to be able to go horseback riding at his ranch by mid-August, when he reportedly hopes to do so, O'Kieffe said, "I think it's possible." But, the doctor added, "I think he may just sit on the horse and have his picture taken."

Questions continued to be raised yesterday that the decision to give Reagan the full colon examination that found his tumor was somehow prompted by knowledge that the president's brother, J. Neil Reagan, 76, had undergone surgery for colon cancer July 3.

Colon cancer tends to run in families.

Speakes said, "the decision for roughly this timing was made before they were aware that the president's brother had had the same type of a polyp removed.