Top government health officials told a Senate subcommittee yesterday that the low levels of radiation carried outside the Three Mile Island nuclear plant site from the accident last week have not endangered the health of area residents and pose no significant risk for the future.

Nonetheless Health, Education and Welfare Secretary Joseph A. Califano Jr., announced his agency would embark on long-term health studies of workers at the plant near Harrisburg, Pa., as well as pregnant women, their children when born and a sample of the general population exposed to radiation over the past week.

At the same time, Califano said monitoring of radiation still in the area would continue and would be made public to reassure the residents.

The long-term studies would be undertaken, Califano said, because there are "great uncertainties that still remain about the relationship between cancer deaths and low-level radiation." The HEW secretary testified that, based on current radiation dose estimates, no additional cancer cases should develop from those exposed outside the plant site.

Subcommittee Chairman Edward M. Kennedy (D-Mass.) had opened the hearing by stating that "part of the fear, concern and suspicion Americans share about this accident . . . stems from the poor track record of the federal government in leveling with the American people about the health effects of low-level radiation."

A controversy has been raging for more than a year among scientists in- side and outside government over what long-term health hazards exist from what were once considered harmless, low levels of radiation.

While voicing gratification that the nuclear accident had not led to immediate, serious public health problems, subcommittee members led by Kennedy sharply criticized the delays that marked the federal government's response to the situation.

Dr. Joseph M. Hendrie, chairman of the Nuclear Regulatory Commission, testified that it was not until Saturday, four days after the accident, that his agency installed its own dosimeters to measure the accumulated radiation levels. Until that time-which covered the heaviest emissions of radioactive gases-Hendrie said the NRC had to depend on the Metropolitan Edison Co., operator of the plant, for offsite radiation readings.

Under questioning, Hendrie also said releases of water into the Susquehanna River with some radioactive content and on Friday, March 30, steam into the air had been done without prior NCR approval.

Kennedy criticized the NCR chairman for allowing the company to make decisions "which pose potential implications for public health without consideration by your agency."

Califano said the Food and Drug Administration was on the scene the day the accident happened, March 28, beginning tests of food and milk in the area. It was not until Monday that FDA, TOO, PLACED SOME 200 DOSIMETERS OUT FOR RADIATION MEASUREMENT.

NCR Chairman Hendrie conceded, We were not as fast getting down to the site as we should have been" and that as a result of the experience "we are going to look very hard at our response capabilities."

"There are changes needed," Hendrie said.

Kennedy charged "the system really broke down" and the ranking minority member on the subcommitteem Sen. Richard S. Schweiker (Pa.) said he was "appalled by the confusion, contradictions and misinformation which characterized the response to the accident and created chaos."

Schweiker also argued that health teams should have been dispatched to the plant area the first day of the accident.

A spokesman for the nuclear plant operators, Dr, Shepard Bartnoff, argued that there should be "some representative of the NCR on site who would be the central focus of all activity" in the event of an accident such as that at Three Mile Island.

Bartnoff also gave the sucommittee readings from the company's dosimeters that raised questions as to just how high the cumulative dose for area residents was.

Califano testified that "based on the NCR's data, the largest dose anyone residing in the area of the plant is likely to have received during the five days following the accident is a total dose of 80 millirems.

Bartnoff, however, testfied that at one site some three-tenths of a mile east of the plant, the dose rate was nearly 2.76 millireems per hour during the period March 29 to March 31-the time of the biggest release of radioactive gases. If that rate continued for the entire 48 hours, as implied by the testimony, it would amount to 132 millirems for two days alone.

NCR officials admitted to subcomittee sources that their data did not contain the company's readings and government sources expected the 80-millirem number to be raised when additional information is received.

Even if it is doubled, however, it still is below the annual radiation from natural background and would keep individuals exposed below the 500 millirems now considered the standard for the general public. CAPTION: Picture, Califano, Hendrie and Environmental Protection Administrator Douglas Costle, left to right, during hearing on Three Mile Island plant monitoring.By James K. W. Atherton-The Washington Post