Calling the Nuclear Regulatory Commission's performance "slow, indecisive, cautious -- in a word, complacent," the General Accounting Office yesterday recommended that the agency take steps to provide "more aggressive leadership" to the public and the atomic power industry.

The GAO also sided with President Carter and against the Kemeny Commission in concluding that a commission is a "superior organization form" for the agency.

The Kemeny panel, set up by the president to investigate last year's accident at Three Mile Island, concluded that the present five-member commission should be scraped and replaced by a single administrator. Carter disagreed, and has said he will submit a plan to Congress that will retain the commission but in a strengthened and streamlined form.

The GAO, Congress' investigatory arm, laid the agency's problems to its having "continued nuclear regulation as it found it" when it inherited the task from the old Atomic Energy Commission in 1975.

The AEC was divided into two agencies, the NRC and the Energy Research and Development Administration, to separate regulation of nuclear power from its development. Critics felt that having both functions in one agency created a conflict.

After their agency's creation, the commissioners "failed to clearly define their roles in directing nuclear regulation," the GAO concluded.

To be effective, it said, the NRC must develop measurable goals and "systems for evaluating the commission's performance," elevate policy-making from the staff level to the commissioners and "define the commission chairman's authority and duties as the commission's principal executive officer."

This last point will be of particular importance, the GAO said, if the commission form is retained. The report found the commission form "clearly superior" to a single administrator setup which, while efficient, would contain "much more potential for abrupt changes in the direction of nuclear regulatory policy."

The report also recommended that Congress "continue to take an active oversight role" because "ultimately Congress must decide" what form the agency should take.

The GAO also said four of the five commissioners "agreed to varying degrees, with the general thrust of the report," and the fifth conceded that the "report contains many justified criticisms."