"This," declared the full-page ad in Friday's Washington Post, "is what they mean by planned parenthood." Underneath was a picture of a fetus next to medical instruments. The caption on the picture said: "She is one of thousands of babies aborted each year in the late months of pregnancy. Photo by permission." The advertising copy that followed began: "They mean abortion is now used for birth control. They mean that unborn babies shouldn't have the right to live . . . not even in the ninth month of pregnancy."

The ad, paid for by the National Right to Life Committee, continued: "Tens of thousands of unborn children are being aborted even after five months in the womb. The chief of the federal Center for Disease Control's Abortion Surveillance Branch recently estimated that 400 to 500 live births follow late-term abortion attempts each year. Most of these survivors are severely injured in the process and soon die . . .

". . . abortion is legally available at any time during the nine months of pregnancy in all 50 states for almost any reason." The ad concluded: "Abortion. You pay for it with your tax dollars. Women pay for it with their bodies. Unborn babies pay for it with their lives."

The advertisement implies that third trimester abortions are used for birth control--a terrible distortion of the facts. Numbers are exaggerated. The real reasons for late abortions are never mentioned. The photograph is designed to shock. It was published under the newspaper's policy of granting maximum leeway to advocacy advertisers. The line is drawn at libel, outright falsehood, illegality and bad taste. The purpose of this column is not to quarrel with that policy, but to attempt to undo public misunderstanding of late-term abortions that the ad fostered.

In 1978, the most recent year for which data is available, more than half of all abortions were performed by the eighth week of pregnancy or before, according to the Alan Guttmacher Institute. Forty percent were performed by the 12th week or before and almost all the rest were performed before the 20th week. Only .8 of 1 percent, or 11,900, were performed after the fifth month. According to the Center for Disease Control, which received data from 38 states, there were 6,401 performed in the 21st week or beyond, also .8 percent of the total. This is not the tens of thousands claimed in the ad, and attributed to the CDC.

Dr. Ervin Nichols, director of practice activities for the American College of Obstetricians and Gynecologists, says the college defines abortion as occurring only when the fetus weighs less than a pound or the procedure takes place prior to the 20th week. "After that, we are talking about premature . . . or preterm deliveries and they are done for one of two reasons: either to preserve the life of the fetus or the life of the mother or both." Not, in other words, for birth control. Furthermore, he said, medical advances have made it possible to terminate pregnancies by delivery in the 28th week and beyond, when the baby or mother are imperiled, and have a 90 to 95 percent survival rate for the infants.

Examples he gave of health dangers included the mother's blood pressure suddenly shooting up, producing serious hypertension or a toxic reaction to the fetus, a mother with severe diabetes, a situation in which the placenta has become lodged over the opening of the uterus and the woman is hemorrhaging to death. He said when a woman has developed cancer of the cervix, pregnancy has to be interrupted to treat the disease or the treatment itself can cause premature labor.

Amniocentesis, a test which shows birth defects and RH blood factor incompatability, is usually done in the 16th to 18th week and test results require two to three weeks of culture growth. That is another circumstance in which defective fetuses may be aborted at the end of the second trimester or very beginning of the third trimester, he said. The reality of the situation is that third trimester abortions are done "strictly for health" reasons, said Nichols. He also pointed out that "not one" of the instruments shown in the photograph is "ever used to do an abortion," although "they may conceivably be used by a pathologist to do a postmortem."

According to Daniel Donehey, public relations director of the National Right to Life Committee, and to other committee advertising that uses the photograph, it was taken by a Maryland pathologist named William Jones. The current Directory of Medical Specialists contains only one William Jones in its listings of Maryland pathologists, William P. Jones, who is listed as on the staff of Suburban Hospital. A spokeswoman at Suburban said he had been an emergency room physician there but now is in private practice, although he retains medical privileges at Suburban. She said he did not practice pathology at Suburban and that there is "no way he Dr. Jones could have come up with that photo in our hospital. A picture like that would create a huge uproar in any hospital if linked to their lab." No hospital would release a photo of a patient or part of a patient without the written consent of the patient or his family and the physician, to protect the privacy of the patient, she said.

With a photograph of an aborted fetus so clearly linked to planned parenthood and birth control in the ad, the question then became why was that fetus aborted. At first, Dr. William P. Jones's only answer to questions about the picture was "I don't wish to make any comment," and "I have no comment." Then he said: "Ask the photographer." Asked again about the circumstances, Jones said, "You'd have to ask the mother or her doctor." Who was the doctor? "I don't know," he said.

Donehey later contacted Jones but the only answers Donehey provided about the abortion were that it was induced with prostaglandin, that the fetus was sent to a pathology lab and that Jones' "best estimate was that the baby was 26 weeks old." They declined to provide further details about why the fetus was aborted, where, when or whether the parent's permission had been obtained for the fetus to be photographed. "This is human garbage under current law, so there is no parent per se," said Donehey.

Dr. Willard Cates, who is in charge of gathering abortion data for the Center for Disease Control, said the National Right to Life Committee ad was misleading in that it conveyed the message that most of the legal abortions in the 1970s would have been completed pregnancies had abortions not been legal. He said abortion figures up through 1975, at least, show those pregnancies would have been terminated through illegal abortions. He also challenged the conclusions of the ad that the public pays for abortion with its tax dollars and that women pay for it with their bodies. State, but not federal, tax monies may be used, he said, and "abortion is a lot safer than childbearing."