The federal official in charge of the Three Mile Island nuclear power plant said yesterday "the crisis is over," and Pennsylvania Gov. Richard Thornburgh said it was safe for pregnant women and small children to return within a five-mile radius of the site.

Thornburgh also lifted the order he issued two weeks ago closing 23 schools within the five-mile radius, and said at a joint news conference that there is no threat to public health from milk or drinking water in the area.

In a separate development, the staff of the Pennsylvania Public Utility Commission recommended that that body delay and reconsider a $49 million rate increase it had granted to Metropolitan Edison Co., principal owner of the Three Mile Island plant.

The increase was sought and granted earlier this year to cover the cost of operating the nuclear reactor that has since been damaged in the accident at Three Mile Island on March 28, the most serious nuclear accident in U.S. history.

Since that reactor is now "unlikely to be in commercial operation for the forseeable future," the staff said, the increase would make the company's rates "excessive and unreasonable."

With the nuclear power plant out of action, Metropolitan Edison has had to buy power from other utilities. It has passed along this cost to its customers. It also has $300 million in insurance to pay for repairs to the reactor.

Harold Denton, the senior federal official at Three Mile Island, said at the news conference yesterday, "I consider the crisis is over today with regard to the status of the core," that part of the power plant where the nuclear fuel rods are.

He also said it would be several more days before the plant could be brought to what experts call cold shutdown, where the temperature in the plant is below the boiling point of water.

Technicians continued uneventfully yesterday to do what they have been doing for about a week now: draw gas, mainly hydrogen, out of the circulating radioactive water that is cooling the reactor.

To cool the reactor the rest of the way, they have to reduce the pressure this cooling water is now under. They fear that unless they draw off the gas first, large bubbles could form when the pressure falls, and these bubbles could themselves be dangerous in several ways.

The engineers are venting the drawn-off gas into the concrete containment building that houses the reactor, and that is now sealed off. Inside the building, the gas will gradually lose its radioactivity.

Thornburgh had been looking to Denton for guidance on the safety question. He said Denton's statement at yesterday's news conference "means that it is now considered safe."

The state Department of Environmental Resources' Bureau of Radiation said yesterday it will begin offering free body radiation detection tests today to "determine whether the normal radioactive content of the people in the area has changed," according to a state official.

In the early days of the accident, the governor advised that pregnant women and small children move out of the five-mile radius because they are regarded as the most susceptible to radiation poisoning.

Thornburgh also said yesterday he was ordering civil defense office to drop down from full-alert to on-call status. But "this does not mean that we will relax our vigil," he said. "We will continue to monitor the entire situation on a 24-hour basis."

Before Thornburgh spoke yesterday, there were still five families, including two pregnant women and nine small children, staying in an evacuation center at Hershey, Pa., about 11 miles from Three Mile Island.

Many evacuees stayed with friends or family who live outside the five mile zone. In all, 965 persons were registered at the two evacuation centers at the state set up after the accident. At least two of the pregnant women who left the area when the governor issued the warning have given birth. Both had girls. CAPTION: Picture, GOV. RICHARD THORNBURGH . . . children, pregnant women may return