The Carter administration is weighing a legislative proposal that would substantially speed up the development of nuclear energy in the United States by streamlining regulatory procedures.

James R. Schlesinger, the President's top energy adviser, yesterday told Rep. Thomas L. Ashley (D-Ohio) and other key members of Congress that the administration has under consideration proposals that would cut to 18 months the regulatory licensing process that now takes up to six years.

Ashley will become chairman of the House Select Committee on Energy after the President announces his energy policy next week.

"We are looking at the licensing process because the existing licensing process is unsatisfactory to everyone," an administration source said. "Explicit in any presidential proposal" he said, "would be an assurance to protect the public interest, regarding health safety and the environment."

Another source said the administration seeks to streamline the regulatory process, now under the administration of the Nuclear Regulatory Commission, by standardizing nuclear power plants and seeking "generic sitting decisions" - decisions covering health and safety standards.

These sources stress that the President has made no final decision on these proposals.

The NRC is an independent regulatory agency that is charged with licensing the construction and operation of nuclear plants and ensuring that they meet health, and safety standards.

During his campaign for the presidency, Carter frequently said that nuclear power should be looked upon as a last resort in U.S. energy planning.

"We are now facing a whole series of last resorts," an administration official said yesterday. That assessment was based on declining U.S. gas and oil resources and the environmental, production and transportation obstacles involved in the widespread utilization of coal.

According to the NRC 65 conventional nuclear reactors are in operation, 71 plants are under construction, and an additional 66 reactors are awaiting construction licenses.

The 65 conventional reactors, nearly all Light Water Reactors, provide 8.7 per cent of the nation's installed electrical generating capacity today.

The Atomic Industrial Forum, a nuclear industry trade association, projects that by 1985 the United States will have 175 Light Water Reactors in operating which could provide 21 per cent of the nation's total electrical generating capacity.

Utility industry sources say that it requires up to two years to collect the necessary data to apply to the NRC for a construction license. The NRC in turn, industry sources say, generally takes an additional two years to make the final licensing decision.

Critics of present licensing procedures point to the significant difference in lead time - an average of 10 years - in the United States, as opposed to seven years or less in Europe and Japan.

In closed-door remarks before an energy conference sponsored by Time magazine in Williamsburg, Va., last week, Schlesinger told a diverse group of industry and public-interest leaders that the United States must build a considerable number of nuclear power plants, which would require simplifying the licensing process.

Should the Carter administration proceed with what is clearly a major commitment to accelerated development of nuclear power, it will undoubtedly face significant opposition from environmentalists. Labor and industry however, have supported an expansion of the nuclear program.

What is needed, Schlesinger said at the Williamsburg meeting last week, is a "social compact" based on the acceptance of common principles by nuclear proponents and environmentalists.

The trade-off for environmentalist would be the conservation of natural resources, including energy, he said. In exchange, nuclear development could go forward under mutually agreeable ground rules.