Nuclear power plants may be required to expand the number of radiation measuring devices they have in areas five to 10 miles from their reactor sites, according to Nuclear Regulatory Commission officials.

Robert B. Minogue, director of the NRC's Office of Standards Development, told a Senate subcommittee yesterday that, as a result of the Three Mile Island accident in March, "the whole question of monitoring networks offsite became a matter we are reexamining with considerable urgency."

Minogue gave the subcommittee maps locating the 20 thermal luminescent dosimeters (TLDs) for radiation measurement that Metropolitan Edison, operator of the Three Mile Island plant, had offsite there.

For the first four days after the accident, during which time most radiation was released, the company's dosimeters were the only devices recording the cumulative dose levels offsite.

Only one company TLD, the map showed, was located in the northeast quadrant more than one mile from the plant.

That is the area that received the most radioactive gas from the major release on March 30.

On March 31, the NRC and other federal agencies began putting in the more than 300 TLDs that now encircle the plant out to 20 miles.

However, with only a few company dosimeters in use and the spot measurements made during the first days of the accident, government scientists are having problems coming up with a final population radiation exposure level.

Sen. John H. Glenn (D-Ohio), chairman of the Senate Government Operations energy subcommittee, asked the NRC officials if current dosimeter requirements are adequate for accident situations.

Minogue responded that most of the TLDs now maintained by nuclear plants are designed "to measure normal effluence." He said they are "adequate" to handle immediate public health needs in an accident situation where a decision on evacuation must be made.

"They are not adequate," he said, "if one wants to make a solid estimate" on the accumulated dose for long-term health projections.

An NRC source said after yesterday's hearing that the commission staff is studying a plan to require nuclear plants to have TLDs located in every population area within 10 miles of a reactor.

The NRC currently requires coverage only in the immediate vicinity - normally on the boundary of the residences closest to the plant.

One week after the Pennsylvania accident, federal officials estimated the cumulative exposure level to the 2 million people living within 20 miles of Three Miles Island at 1,800 Person-rems. (A person-rem is the average radiation level for the entire area multiplied by the number of persons living there.)

Last week, various officials said their first estimate had been doubled based on a reanalysis of the data and the limited number of dosimeter readings.

Health, Education and Welfare Secretary Joseph A. Califano Jr. put the level at 3,500 person-rems, but said it probably would go higher.

At that level, Califano said there could be one additional cancer death and one additional non-fatal cancer case among the 2 million inhabitants.

NRC Chairman Joseph Hendrie is scheduled to appear before the Glenn panel today.