Doctors conducting an annual examination of President Reagan pronounced him in "excellent" health yesterday but said they had found a second benign growth in his large intestine and evidence of blood in stool samples, conditions that bear further watching.

A written White House statement said the results of Reagan's general physical last week at Bethesda Naval Hospital indicated that two of four tests for hidden, or "occult," blood in the stool were positive. It said that physicians believe that this may be from the newly discovered growth, or polyp, or from diet, and "will be monitored."

"All other tests were in the normal range," the statement said.

Outside physicians said the significance of the stool blood test results could range from nothing of consequence -- a false alarm -- to a sign of an undetected growth that might potentially be cancerous. But they emphasized that it was far too early to tell how medically meaningful the findings were.

Capt. Walter Karney, an internist participating in the exam Friday, said in the statement that "President Reagan continues to enjoy good health. His overall physical and mental condition is excellent. I am especially impressed with the fact that his blood pressure is lower than a year ago -- this is quite remarkable."

Reagan, who turned 74 on Feb. 6, is the oldest president in U.S. history.

His last complete physical examination took place last May 18 after a 2 1/2-year gap, and a small growth or polyp -- less than one-fifth of an inch long -- was discovered in his large intestine, partially removed and later determined not to be cancerous. Stool blood tests then were negative.

The polyp discovered in this year's exam, described in the statement as a "small inflammatory pseudo-polyp," was similar in size and location to last year's growth, according to White House spokesman Larry Speakes.

The statement said that a procto-sigmoidoscopic examination, a test in which an optical instrument is used to examine the lower end of the colon, revealed no signs of the polyp seen last year but did show signs of diverticulosis, a condition commonly found in older persons in which there are tiny pouches in the wall of the colon that may cause no medical problems.

Speakes said the new growth was one in which there was "zero incidence" of cancer. But he said doctors plan to conduct follow-up blood tests on stool samples to better determine what might cause Reagan's hidden bleeding.

One possibility, according to Speakes and medical experts, is that it is simply a "false positive" resulting from food consumed before the test. Speakes said Reagan will be put temporarily on a special American Cancer Society diet to restrict red meat and certain vegetables before retesting occurs.

Otherwise, he indicated, the tests could indicate bleeding from the new growth or from undetected polyps.

Dr. Donald A. O'Kieffe, a Washington gastroenterologist, said that, generally speaking, tiny polyps of the kind discovered in the recent exam were unlikely to cause bleeding. If repeat testing still indicates bleeding in the stool, "the first thing we would be concerned about is whether there are additional polyps in the colon that haven't been revealed yet."

To determine this, he said, additional tests likely would be done, ranging from a more extensive examination of the entire colon with a flexible optical instrument, or colonoscopy, to a barium enema, involving an X-ray exam of the colon. If larger polyps were discovered, they would be tested to determine if they were cancerous or noncancerous.

O'Kieffe noted that a positive test for blood in the feces could be "a warning signal today for early cancer." But he added that "in someone who has been watched as carefully as Reagan, the likelihood it represents something serious is low."

Although colon and rectal cancers are the second most common cause of cancer death, the cancers are highly treatable when detected at an early, localized stage. The American Cancer Society recommends a digital rectal examination annually after age 40 and an annual stool blood test after age 50.

Dr. Dennis O'Leary, a George Washington University School of Medicine dean who served as a spokesman after Reagan was shot in a 1981 assassination attempt, noted that the blood in the stool test was only a "screening test that can be significant or may not be significant . . . . If there was more than a trace of blood in the stool, it is a potentially worrisome signal that needs to be followed up."

O'Leary agreed that Reagan's current blood pressure reading of 130 over 74 was excellent for his age. "I wish I had blood pressure like that when I'm 74."

O'Kieffe and O'Leary emphasized that they were speaking in general terms and not familiar with detailed findings of the Reagan physical.

Yesterday's White House statement also noted that Reagan continued to suffer from a contraction of one of the tendons on the ring finger of his left hand, a condition known as Dupuytren's contracture. Speakes said there were no plans to surgically correct it. He said it bothers the former cowboy screen star, who has a fondness for his California ranch, only "when he twirls his pistol to put it back in its holster."