Four members of a scientists' panel said yesterday that a federal law is needed to protect the public from unwise tinkering with human or animal genes.

The scientists spoke at news conference here as the National Academy of Sciences opened a three-day public forum on the new field of genetic manipulation.

The National Institues of Health in June issued safety guidelines to cover scientists doing genetic research with federal funds. But several private firms, including drug companies, are entering the field, and the guidelines do not cover private industry.

Also, some experiments are so simply, one scientist said, that they might be done by a bright high school student "in Garden City, Kan.," just "to see if he could."

"The time has come for some federal regulations," said Dr. Daniel Callahan, director of the Hastins, N.Y., Institute of Society, Ethics and Life Sciences.

"If there is no federal legislation then every city, like Cambridge Mass., will make its own rules," said Dr. Daniel Koshland, University of California at Berkeley biochemistry chairman.

This prompted Cambridge Mayor Alfred Vellucci, who called himself "an univited visitor," to speak up. Last month Vellucci tried to outlaw in Cambridge all research that combines the genetic material of various species. But the city council of Cambridge, where Harvard and Massachusetts Institute of Technology are located, overruled him and allowed most, but no all, such research.

"No scientist has said he can guarantee that the work is safe," Vellucci complained. "We've sent a letter to Sens. [Edward M.] and [Edward W.] Kennedy, Brooks and Congressman [Thomas P.] O'Neil, who represents out city, telling them they'd better hurry up and pass laws to control what goes on - and what crawls out of these laboratories."

The scientists agreed that they cannot guarantee safety, but most said the risks are almost certainly small and acceptable as long as certain experiments prohibited by the NIH guidelines are avoided.

Dr. Erwin Chargaff of Columbia University said he thinks much of the work is potentially unsafe but backed federal legislation, "though I don't think it'll do much good."

"My guess is that a law will be needed," said Dr. David Hamburg, head of the science academy's Institute of Medicine. NIH's Dr. Maxine Singer said a federal interagency committee is considering whether a new law is needed or whether some federal agency has regulatory power. She indicated that she would accept its recommendation.

Only Dr. Paul Berg of Standford University and Dr. Alexander Rich of MIT said that they still hope that "some other mechanism" than a new law or regulatory agency can be found to maintain safety.