Three scientists yesterday called for a halt to the creation of new life forms in laboratories, charging that such research is a "threat to future generations" and the start of "genetic engineering" that would change human beings.

They joined a growing group of biologists and others who are questioning biology's newest technique: combining the genes of different organisms to study life and develop drugs or other products.

The three - Drs. Ethan Signer of the Massachusetts Institute of Technology and Jon Beckwith and George Wald of Harvard - spoke at a National Academy of Sciences public forum on the new research. Beckwith, in his speech, called only for wide discussion before scientists continue the genetic research, but added at a news conference: "I'd vote to stop."

The trio was joined at the NAS forum by three others who have voiced similar concerns: Drs. Robert Sinsheimer, California Institute of Technology biology chairman; Erwin Chargaff of Columbia University, and Jonathan King of MIT.

King also urged a halt to the work. Sinsheimer and Chargaff suggested protected national laboratories to prevent spread of any unexpected new disease organisms, though Chargaff said, "I would like to top the work if I could but I cannot."

Also voicing concern were other citizens, including Jeremy Rifkin of a Washington lobby called the People's Business Commission. Many called for wide public debate before researchers enter what Sinsheimer called "man's largest step into the unknown" since scientists split the atom.

The doubters are still minority among biologists. But there have been public protests over the research in Cambridge and San Diego and at the University of Michigan and Princeton. Congressional health subcommittees are planning hearings to consider federal regulation.

The objectors at the NAS forum here spoke of the danger of unexpected new diseases and of the day when doctors can insert altered genes into human beings to change them or their children.

Signer charged that such practices "will lead us to the excesses and dangers of human genetic engineering."

These warnings were countered by a far greater number of biologists who said the work has done no harm so far and the chance that it could do any seems remote, that they are not doing genetic engineering but smallscale experiments, and that society can and should halt any genetic work that it does not desire.

Dr. Daniel Callahan, director of the Hastings, N.Y., Institute of Society Ethics and Life Sciences, said that although he thinks researchers have so far been careful and prudent, he believes "full public debate" is needed on the possible dangers that the doubters raise.