Two public interest groups on Saturday assailed proposals for moving ahead with a new generation of nuclear power reactors to meet the challenge posed by the "greenhouse effect."

They called instead for greater emphasis on energy efficiency, conservation, renewable energy sources and natural gas to help cope with the global warming trend largely caused by the burning of fossil fuels."Nuclear power cannot solve the global warming problem," said a report issued by the Washington-based groups, Public Citizen and the Safe Energy Communication Council, both of which have long criticized the nation's nuclear power industry.

The study said, "High costs, coupled with environmental and safety shortcomings and long construction time, eliminate nuclear power as a credible option for reducing carbon dioxide emissions from coal- and oil-fired electrical generating plants.

"On the other hand, investments in energy efficiency improvements, con-servation, renewable energy and selected natural gas technologies would be far less expensive and environmentally safer. In addition, they would yield results in a shorter time frame than nuclear power development," it said.

Scott Peters, a spokesman for the U.S. Council for Energy Awareness, a nuclear industry group, responded that "the Department of Energy has forecast that 100 gigawatts in additional, new capacity will be needed by the year 2000. And the only way we can get that is by using everything we can - nuclear, coal, gas, solar, whatever we can find, including conservation or efficiency."

The report by Public Citizen and SECC said, "The nuclear industry is exploiting global warming as an opportunity to revive support for a new generation of nuclear reactors."

Edward Davis, president of the American Nuclear Energy Council, the nuclear industry's principal lobbying arm, testified recently at a congressional hearing that "nuclear energy must be revitalized in order to alleviate the greenhouse effect."

Three bills introduced in the Senate to deal with the greenhouse effect would provide substantial federal support for development of next-generation nuclear power plants.