The Department of Health, Education and Welfare proposed regulations yesterday that for the first time would provide specific protection for children used in medical and behavioral research projects.

The proposals leave open the question of at what age the consent of the child as well as a parent or guardian should be required.

HEW Secretary Joseph A. Califano Jr. said he was adopting most of the recommendations on children made last January by the National Commission For the Protection of Human Subjects of Biomedical and Behavioral Research.

The commission estimated that in fiscal 1975, children were involved in 3,460 research projects that cost the government $391 million.

Most involved research in education, including some routine tests and questionnaires given schoolchildren. but some diseased children receive experimental drugs and undergo other experimental techniques in research sponsored by the National Institutes of Health. Children, like adults, also are given test vaccines before immunization programs are launched.

The government also funds studies of mentally retarded youngsters.

Although there are no specific present ground rules for tests on children , the commission said most projects seek permissions from the child's parent or guardian. That would continue under the new rules, but the child might have to be asked as well, the Commission had recommended that assent be sought from children age 7 or older, as the American Pediatric Society recommended.

Califano called for public comment "on whether HEW should establish a specific age - for example, 7 or 12 - after which a child's own agreement to participate in research would be required, or whether the need for assent by the children involved should be determined on a case by case basis for each research project."

The proposed rules, which will be subject to public comment over the next 60 days, would require special boards at the institutions conducting the research to review each project to make sure they include safeguards for the children.