The Cambridge City Council voted unanimously Tuesday to extend its three-month moratorium on controversial "recombinant DNA" research at Harvard and the Massachusetts Institute of Technology (MIT) for an additional three months.

Last night, George Wald, Higgins Professor of Biology, and Mathew S. Meselson, chairman of the Biochemistry Department, debated the risks and merits of the proposed containment laboratory for recombinant DNA research before 500 people at the Cambridge Unitarian Church.

The Council's decision to extend the moratorium initiated last June in the wake of extensive public controversy over the research was made partly because the council wants to see an environmental impact statement by the National Institute of Health (NIH) before it permits the research, a statement accompanying the Council's decision said.

Daniel Hayes, chairman of the Cambridge Laboratories Experiment Group, said the extension of the moratorium was "mutually-agreed upon" by University scientists involved in the experimentation and members of his group.

Hayes said his group presented the proposal to extend the moratorium to the council earlier this week as a fait accompli, "but if the mayor wants to say he's responsible, that's o.k. with me."

The Council's original resolution to initiate a recombinant DNA research moratorium in June followed considerable local and national debate on the potential environmental consequences of such research.

Among the proposed experiments that have sparked heated debate are those which would examine genetic control mechanisms in higher-level organisms.

In these experiments, researchers would transfer loose strands of DNA--the basic molecular unit of heredity--from warmblooded animals into specimens of E. coli, a commonly-utilized laboratory bacterium, in hopes of producing a new species with heretofore unknown characteristics.

At the debate last night, Meselson emphasized that in nature DNA is always recombining and mutating, "constantly making new connections" on its own.

Afflicted with laryngitis. Meselson soothingly discussed the NIH safety guidelines and pointed out the advantages of being able to do DNA research in "a more or less directed way" in the laboratory.

Wald said today's scientists have the ability to cross wide natural boundaries to merge disparate organisms overnight.

"We're asked to turn over the products of three billion years of evolution to a group of scientists eager to play around with them," he said.

Meselson said scientists would not be creating whole new species, just individual new organisms. He said that those organisms would have to face "a competitive struggle for every available ecological niche."

Wald said he was less sure of mankind's chances in such a competitive struggle and advocated isolating the containment laboratory, in which the controversial research would be controlled in a relatively unpopulated area. He said laboratory workers and their families should be closely monitored because they would exhibit effects first.

Meselson said that in the last 50 years no one who was not connected with a laboratory had been infected by research organisms.

But Wald said that the Biolabs, the site of the proposed containment facility, are 50 years old, and ant-infested. Even the most elementary precautions would require insect control, he said, adding he believed the Biolab ants are ineradicable.

Wald called the extension of the moratorium "very important but largely symbolic. The actions of Mayor Vellucci and the City Council have been very important because this is the first City that has raised the issue publicly and acted upon it."

Meselson said he was "fully sympathetic" with the extension. "I have no objections to the Review Board taking a reasonable amount of time to study the problem."

Barbara Ackermann and Francis Duehey, two Cambridge city councillors, and David Baltimore and Jonathan King, two MIT professors, also spoke at the forum.

Ackermann opposed the experimentation, although she said the experiments will probably be permitted, so they should go on under the aegis of "a Harvard or an MIT"--but not in a "happy-go-lucky student building," such as the Biological Laboratories