Nancy Reagan's malignancy did not spread beyond her left breast, making prospects for a full recovery virtually certain, final test results showed yesterday.

"Mrs. Reagan is recovering remarkably well from surgery," said Dr. John E. Hutton, the president's physician, in a statement released by the White House. "The medical team visited her this morning and we are satisfied with her progress in every respect."

Telling reporters that he "had a date with a girl out at Bethesda," President Reagan traveled by helicopter to Bethesda Naval Medical Center yesterday morning to visit Mrs. Reagan and await the test results.

He carried with him a gift of a mirror the First Lady had once admired, wrapped brightly in red, white and blue.

Together, the couple telephoned Chip and Reba McClure, the parents of Jessica McClure, to "express their happiness" at Jessica's rescue from her ordeal in an abandoned well in Midland, Tex.

Hutton said final analysis of tissue and lymph nodes removed from Mrs. Reagan during a 50-minute modified radical mastectomy on Saturday revealed that there was no "further malignancy or evidence of other disease." He said that other than routine examinations, no further treatment is envisioned.

Because the cancerous lesion was only 7 millimeters in length, about a quarter of an inch, medical experts had predicted that it was unlikely to have spread to her lymph nodes.

"This confirms all the best hunches," said Dr. William F. Feller, an associate professor of surgery at Georgetown University Medical Center. "You couldn't ask for a better prognosis. The key result is that the malignancy was not invasive."

Feller said that medical care for Mrs. Reagan will probably concentrate on arm exercises over the next few weeks to restore her arm muscles to normal strength.

After that, Mrs. Reagan will probably undergo mammograms twice a year, doctors said. Elaine Crispen, the First Lady's spokesman, said that Mrs. Reagan hoped her experience would "encourage people to have early exams."

Yesterday, Mrs. Reagan felt well enough to rise by 8 a.m. and have her usual breakfast of juice, papaya, bran cereal and decaffeinated coffee, according to a White House spokesman.

Doctors said that she could leave the hospital within five to seven days, possibly sooner.

Although some physicians suggested that choosing mastectomy was an extreme treatment, White House spokesmen said again yesterday that Mrs. Reagan was fully aware of her options and made a choice.

It has become increasingly common in recent years to treat small 'Having regular mammograms helped cure her of this disease.'

-- Dr. John E. Martin

malignancies such as Mrs. Reagan's by removing the lesion and following up with a six-week course of radiation therapy.

"The type of procedure is not what people should be dwelling on here," said Dr. John E. Martin, a professor of radiology and a mammography specialist at the University of Texas M.D. Anderson Hospital Tumor and Cancer Institute. "The real news here is that having regular mammograms helped cure her of this disease. That is the message that should go out to thousands of women in this country."

Fewer than 5 percent of all breast cancers are found at a stage as early as the one doctors discovered in Mrs. Reagan's left breast. More than 70 percent of breast cancers are discovered by women themselves, according to the American Cancer Society. When a tumor is large enough to feel it is also more likely to have spread to the lymph nodes.

Breast cancer is the second most common cause of cancer death in women, following lung cancer.