The Tennessee Valley Authority announced yesterday a series of "far-reaching changes" in its nuclear power plant operations, including lowered radiation exposure limits and intelligence testing for all plant operators.

Most of the changes go beyond federal reules and will affect TVA's three existing reactors at Brown's Ferry in Athens, Ala., and 14 more that it has planned and under construction in three states.

The shifts, recommended by a six-member in-house task force in the wake of the Three Mile Island accident, could be useful in the rest of the nation's power reactors as well, said S. David Freeman, TVA chairman. "We are in a unique position to provide an example," he said. "The other reactors are operated by electric utilities who are in business only to produce power."

TVA, the nation's largest power producer, is a quasi-governmental agency set up in the 1930s to bring energy and development to a depressed seven-state area of the Tennessee River valley. Freeman is considered a possible successor should Energy Secretary James R. Schlesinger leave.

The task force's 60 pages of changes include:

Lowering of rafiation exposure limits for TVA nuclear power plant personnel to four rems per year. This is 20 percent less than the five-rem level currently imposed by TVA and far below the Nuclear Regulatory Commission's 12-rem limit.

Intelligence testing for all TVA power plant operators. No specific test has yet been chosen and no minimum IQ set, the task force said, but future certification will be contingent on the test and on 36 months of training. The previous standard was 22 months of training.

A bureaucratic shakeup that takes nuclear safety revuew out of the hands of power production management and puts it under a special safety review team with direct access to TVA top management.

Design changes in the TVA reactors - especially those resembling the one at Three Mile Island - to rule out misleading interpretations and other operator reactions that worsened the Three Mile Island accident.

Evacuation planning for persons living within 10 miles of the TVA plants. Current standards call for plans in a three to seven-mile range.

Asked whether the inclusion of intelligence testing said anything about TVA's view of the Three Mile Island operators, Freeman responded that it did not but that the accident had taught TVA many lessons.

"While this report was put together rapidly, it is not superficial," a task force member said. "It is certainly not the end of our nuclear safety efforts," Freeman added later.

The design changes being put into effect are among those that TVA engineer Caryle Michelson has already recommended to the Nuclear Regulatory Commission in his role as consultant there.

They will include some kind of direct instrument reading of the water level in the radioactive core of the reactor, a lack at Three Mile Island that led the operators to allow the core to overheat. Automatic closure of all water lines out of the reactor building will prevent the escape of radioactive spillage that occurred at the Pennsylvania plant.

The hydrogen buddle that accumulated at the top of the Three Mile Island reactor could have been vented safely with a vale that TVA will install at the top of each unit. New instruments will tell operators whether crucial valves are shut or open and whether they ought to be. Radiation sampling and testing will be easier, while computer codes will be modified to provide a clearer analysis of what is going on inside the core.

Michelson said yesterday that industry awareness of what happened at Three Mile Island meant that chances of another similar accident are now "quite small."