Surgeons at Bethesda Naval Hospital removed Nancy Reagan's left breast yesterday after discovering a small cancerous tumor. The White House said the operation was without complications and preliminary tests showed that the cancer had not spread.

"I'm glad that this is over and it certainly shows the value of regular checkups," spokeswoman Elaine Crispen quoted the First Lady as saying after the operation.

"She feels just fine," President Reagan told reporters as he returned to the White House after visiting his wife. "Everything was like that," he said, flashing an "Okay" sign with his hand.

Dr. John E. Hutton, the president's physician, said in a written statement that Nancy Reagan was resting comfortably after the 50-minute operation and that her "vital signs are strong and stable."

Crispen said that except for occasional naps, Nancy Reagan was alert and awake, had asked for vegetable soup and gelatin for dinner, and planned to eat the meal sitting in a chair in her hospital suite. She is expected to be walking today, Crispen said.

White House spokesman Marlin Fitzwater said a biopsy revealed the presence of a "noninvasive intraductal adenocarcinoma," which he said was a common form of breast cancer found in the milk ducts. The cancer was approximately 7 millimeters in size, which was "anticipated," Fitzwater said, and it was "concentrated in an identifiable area." The procedure involved removal of the breast and the lymph nodes under the arm.

Hutton said the preliminary laboratory examination of frozen sections "shows no evidence of malignancy in the lymph nodes or surrounding tissue."

The president was driven to Bethesda early yesterday morning, carrying a tote bag that he said contained papers. Dr. Richard Davis, Nancy Reagan's brother and a Philadelphia neurosurgeon, handed him about two dozen pink roses, which the president carried to the First Lady.

At the hospital, Reagan was informed of the biopsy results by Hutton and Dr. Oliver Beahrs of the Mayo Clinic. "Take good care of her," he told the doctors, according to Fitzwater. The president remained at the hospital while the surgery was performed and was reunited with the First Lady in the recovery room, joined by Davis.

"Honey, I know you don't feel like dancing, so let's hold hands," the president said, according to Hutton's statement.

Reagan said on his return to the White House that he "expressed my great happiness" to his wife after the successful operation. He said he did not know when she would return, but she would not be hospitalized long and is experiencing "normal discomfort after an operation, nothing beyond that."

Fitzwater said Friday that Nancy Reagan is expected to remain in the hospital five to seven days. He said there is no plan for reconstructive surgery or any additional treatments. More tests are expected to be completed today. Fitzwater said a White House prognosis would await completion of the tests.

Surgeons interviewed yesterday said that after an operation like the one Nancy Reagan had, patients experience some pain for several days, particularly in the area of the armpit where the lymph nodes have been removed. The pain is usually easily relieved with medications, they said. Most patients are able to leave the hospital after about five days.

A woman recovering from a mastectomy can resume most of her normal activities after three or four weeks. But doctors will probably advise Nancy Reagan to wait for about six weeks before going horseback riding or engaging in other strenuous exercise, experts said.

Nancy Reagan had discussed "all other alternatives" for dealing with the cancer before the biopsy yesterday, according to the White House, so the physicians moved quickly into surgery when the cancer was found.

In taking this route, the First Lady chose the most aggressive option for removing the cancer, medical experts said. Another possibility would have been removal of only the tumor, followed by lengthy radiation treatments, but a White House official said the First Lady wanted to avoid drawn-out procedures.

The surgical team was headed by Dr. Donald McIlrath of the Mayo Clinic and included Beahrs, Hutton and Capt. Harry B. Etienne, chief of general surgery at Bethesda Naval Hospital. Fitzwater said 12 physicians participated, but some were not identified.

The White House refused reporters' requests to question the physicians attending the First Lady. This has been the White House practice since the president's 1985 cancer surgery, when his physicians discussed the details of the operation in a highly public fashion that upset Nancy Reagan.

The White House has instead relayed medical information through Fitzwater and other press office officials, and has issued written statements from Hutton.

Crispen said Mrs. Reagan had received flowers from the public and many world leaders, including King Fahd of Saudi Arabia, President Hosni Mubarak of Egypt and Queen Noor of Jordan. British Prime Minister Margaret Thatcher sent a cable.

Former First Lady Betty Ford, who had her right breast removed at the same hospital 13 years ago, telephoned Nancy Reagan Friday to express her support and best wishes, according to Crispen.