Former president Richard M. Nixon had a skin cancer removed from the back of his left ear eight days ago, two days after President Reagan had the same type of skin cancer removed from his nose, according to the doctor who performed Nixon's surgery.

Nixon's tumor, a basal cell carcinoma, measured about one inch in diameter and probably had been present for several years, according to Dr. Philip G. Prioleau, an assistant professor of medicine and pathology at the New York Hospital -- Cornell Medical Center. He removed Nixon's growth in an outpatient procedure Aug. 1.

In the days following the operation, Nixon suffered excessive bleeding at the site of the surgery because he resumed taking a blood-thinning medication that he had stopped taking just before surgery. The medication had been prescribed by his internist to prevent a recurrence of phlebitis, which he suffered in 1974, Prioleau said.

Prioleau said the bleeding, while not dangerous, did cause accumulation of blood beneath a skin graft at the surgical site. The former president returned to his office Wednesday to have this complication treated.

Prioleau said that during the operation he removed a margin of normal skin surrounding the cancer, as well as a piece of the underlying ear cartilage. He said it is unlikely that the tumor will recur, but he plans to check Nixon every few months.

The skin cancer was removed by a procedure first developed by Frederick Mohs, a Wisconsin surgeon, in which sections of growth are examined microscopically during the operation to make sure the entire tumor has been taken.

Prioleau said Mohs' technique has about a 96 percent cure rate for basal cell carcinoma, and is considered the optimal treatment, but, "Behind the ear is one of the sites where recurrences are greater."

Prioleau said Nixon had noticed "a little bleeding" behind his left ear at times during the last year, but "it's a site you can't see in a mirror, and he didn't realize what it was."

Nixon's spokesman said that on Wednesday, when the bleeding complication was discovered, Prioleau ordered Nixon not to attend a dinner in his honor that evening given by Han Xu, the new Chinese ambassador.

Basal cell carcinomas are the commonest type of skin cancer, with about 500,000 cases occurring in the United States yearly, according to Dr. Perry Robins, associate professor of dermatology at New York University and chairman of the Skin Cancer Foundation.

Although 90 percent of basal cell carcinomas occur on the head or neck, the area behind the ear is a rare location, Robins said. He said most basal cell carcinomas are thought to be due to sun exposure, prompting Reagan's statement at a Monday news conference that he wanted to "convince people to stop broiling themselves in the sun."

Prioleau said Nixon's skin cancer may not have been caused by sunlight. "Behind the ear is not an area in which you get much sun," he said. He said a few such tumors occur in areas not exposed to the sun, but it is not known why.