Nancy Reagan underwent minor surgery at the White House yesterday morning to remove a small growth above her upper lip, press secretary Sheila Tate said.

Tate said a biopsy would be performed on the tissue and that the results are expected to be known tomorrow. She described the abnormality as keratosis, "an area of skin marked by overgrowth of tissue of a different texture, a thickening of skin."

Tate quoted Dr. Daniel Ruge, the White House physician, as saying the growth was "not uncommon."

Surgery was performed at 10 a.m. under a local anesthetic in Ruge's White House office by Dr. Diane Colgan of Bethesda, a plastic surgeon whom Ruge recommended. Tate said four stitches were required to close the area, which was dressed with a small bandage.

Tate said the surgical procedure was the first Mrs. Reagan had undergone on her face and that it was not yet known whether there would be a scar. She said a scar on Mrs. Reagan's right temple is from the use of surgical forceps at birth.

Tate described the first lady as "feeling fine" immediately after yesterday's surgery, which the president did not attend. He continued his work schedule in the Oval Office. The Reagans' son Ron, and his wife Doria, who had been at the White House for the weekend, remained until the surgery was completed, then returned to New York.

Dr. Thomas Nigra, a dermatologist at the Washington Hospital Center, told the Associated Press that such growths, when located on an exposed area such as the face, usually are caused by exposure to the sun.

He said there might be one chance in 100 that Mrs. Reagan had contracted a skin cancer, which he described as "the most common form of cancer and the most curable.

"The risks are minimal," he said, and after hearing the White House description of the surgical procedure, said, "It's probably already treated."

In the afternoon, Mrs. Reagan entertained nearly two dozen members of her East Wing staff at a Christmas party in the upstairs family quarters. Serving eggnog, punch and cookies, the first lady exchanged gifts with the group.

She gave each staff member a rectangular-shaped, beveled crystal etched with a rendition of the White House, her name and the date. The staff gave her a 19th-century plate imported from China. It is called "Lowestuft," and was found on the bottom of a stack of plates in a Georgetown antique shop.