First Lady Rosalynn Carter was pronounced "just fine" by the White House yesterday after an hour-long gynecological procedure at Bethesda Naval Hospital.

The operation was a "D&C," or dilation and curettage - dilating the opening of the womb, then scraping out the membrane that lines it.

The White House would not disclose the reason for the usually minor surgery, and Mrs. Carter's press secretary, Mary Hoyt, called it a "routine" and "private matter."

In a woman Mrs. Carter's age - she will be 50 Thursday - the operation is usually done to seek and possibly correct the cause of excess bleeding.

In something less than one case in 100, the cause turns out to be cancer "and this is what every physician wants to rule out," said a doctor not associated with Mrs. Carter's treatment, Dr. Benny Waxman of George Washington University.

The fact that Mrs. Carter was called "fine" seemed to rule against cancer. And at a few minutes after 6 p.m. the President called for her, and they flew by helicopter directly from the hospital to Camp David for the rest of the week.

If there were any immediate indication of cancer, she probably would have been kept in the hospital for more tests, medical sources said. However, doctors study any material that is removed, and it is unlikely they could completely rule out cancer until sometime today at the soonest.

In late April, Mrs. Carter had a suspicious lump removed from her breast. It proved to be non-malignant.

On June 11, she was ill briefly in Caracas, Venezuela. But she merely had some nausea and dizziness, she said, and reporters saw her resume her active South American tour after a rest of hardly an hour.

Doctors do D&Cs for many reasons - from performing abortions to cleaning the uterus after a miscarriage - as well as for several diagnostic and therapeutic purposes. The most common reason in a woman, 50, is to track down the cause of abnormal bleeding during or between menstrual periods, or after menopause, Waxman and other doctors agreed.

Not even counting abortions, "D&Cs are our most common gynecological operation, about 15 to 20 per cent of our 10,000 surgical procedures a year," said Dr. John Marlow of Columbia Hospital for Women.

The cause of any bleeding may be excess hormone output by the ovaries. Or it may be some benign or non-canor hyperplasia (excess growth) of the uterine lining, or fibroid tumors.

Any such growths are usually removed as part of the operation.

Mrs. Carter was advised to have yesterday's operation "two or three weeks ago, and we just scheduled it when she could do it," Mrs. Hoyt said.

The First Lady went to the operation room at 6:30 a.m. and returned to the Presidential Suite at 7:50 a.m. Dr. Douglas Knab, Naval Medical Center obtsetrics-gynecology chief, performed the brief operation.