A federal advisory commission said yesterday that medical scientists should not be allowed to involve children seven and older in medical or behavioral research unless the children themselves - and not just their parents - first give permission.

The unanimous recommendation - one that breaks new ground in medical ethics - will be sent to Health, Education and Welfare Secretary Joseph A. Califano Jr. by the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research.

If he accepts it, it will directly affect an estimated 175,000 children and minors now taking part in nearly 3,500 federally funded health studies at hospitals, medical centers and mental and other institutions all over the country.

It could also affect thousands of other youngsters, even those getting new experimental drugs in the offices of authorized doctors, since this commission has rapidly been emerging as a leading force in setting new medical rules.

The author of one study on children and consent - Dr. Barbara Korsch of Los Angeles Childrens' Hospital - said in an interview yesterday that "the way it works now in most places is that if the doctor and parents agree that a child should participate, they most likely inform rather than ask the child. If the child's consent has been asked, it has been cursory."

"I'm delighted with the commission's recommendation," she added, "though I would have put the age of assent a little higher, at 9 or 10. Of course a lot of my colleagues won't agree. Some call this commission the 'Commission for the Prevention of Research.'"

The commission was created by Congress three years ago to deal with such questions as how much research should be permitted on living fetuses about to be aborted - or in some cases just aborted; the ethics of research on prisoners and the extent to which doctors can do psychosurgery In all these fields it has urged severe limits.

But none of its recommendations has so far potentially affected as many persons. Research on children ranges from new treatments being tried on those with severe diseases like cancer and leukemia to tests of new vaccines to scores of behavioral and psychological studies.

Often the research cannot help the cooperating subject, healthy or sick, but many produce new knowledge that might help others. And this may require tests that invade the body and often put the subject at some degree of risk.

The University of Michigan Survey Research Center interviewed 471 researchers and 144 subjects or their parents or guardians for the commission, and found that in half of the cases involving subjects 12 or younger, no one directly asked the child's consent.

"I think most researchers, certainly most pediatricians, do ask the child's permission already, at least in a context of winning the child's cooperation," Dr. Kenneth Ryan of Harvard University, commission chairman, said at the National Institutes of Health in Bethesda, site of the commission's meeting.

"What we've come to believe now is that children do have rights, and that at an age when the child can appreciate what's going on and can respond appropriately, the child has a right both to be asked, 'Do you want to do this?' and to say, 'No, I don't.' And the only time anyone has the right to override this is when it's a matter of essential therapy."

The nine members of the 11-member commission present yesterday - doctors, medical and law professors and medical ethicists - voted that:

Before a child or minor is included in any research, a review board at each center should be sure responsible staff members have obtained not only the usual parental permission but also the child's "assent," whenever the child is capable of understanding the research and giving assent.

"A child's deliberate objection to participation . . . should be binding unless the research holds out to prospect of direct benefit that is important to the health or well-being of the child" and offers a treatment or test the child can't otherwise get.

"Capable" was defined as meaning of age 7 or older and not mentally or otherwise disqualified. The commission used the word "assent" rather than "consent," because almost all states set 18 as the legal consent age for most purposes.

Commission members reached no conclusion on another question that has vexed them for months: Whether it is ethical, whether or not a child and parents consent, to include a child in research that has any risk if the study can't possibly benefit that child but may help future ones.