President Carter flew to Pittsburgh yesterday to "see firsthand" how a severely cold winter has affected one of the nation's largest industrial regions.

What he saw was unsettling, he said.

A Westinghouse plant employing 9,000 workers temporarily shut down because of a weather-induced shortage of natural gas. Dozens of barges anchored in solid ice in the Monongahela River - a 128-mile thoroughfare normally used in transporting rich soft coal from southwestern Pennsylvania mines to Pittsburgh steel mills. Churches shut down on a Sunday because they lacked the fuel to keep their congregations warm.

Carter said that his brief helicopter trip also was a symbolic gesture, made "to give the people of our country some feeling of assurance that the federal government - working with local and state governments and private industry - can deal with an energy shortage brought about in a crisis stage by unusual weather."

But in Pittsburgh and after his return to Washington yesterday afternoon, he warned that it would take more than symbols and crisis measures to fulfill the nation's energy needs now and in the future.

The fuel problems affecting the Northeast and the Midwest are merely symptomatic of a "permanent, very serious energy shortage," Carter said at the White House.

"The crisis might be over in a few days or a couple of weeks. But the energy shortage is going to be with us. It's going to get worse instead of better," he said.

Carter, wearing a heavy coat, blue sweater, oxford shoes with lug soles - and, he said, thermal underwear - spoke to reporters outside the South Portico of the White House.

He again urged Americans - in a more insistent tone - to lower their thermostats - to as low as 50 degrees for homes with fireplaces.

"Every houshold that keeps its temperature too high or that wastes fuel contributes to the unemployment of American people and the damage of our society," he said.

Carter said his immediate concern is to get congressional approval of legislation that would give him temporary authority to order natural gas pipelines to shift their supplies to areas of greatest need. The proposal also calls for the temporary removal of price controls in order to move unregulated intrastate gas into hard-pressed interstate pipelines.

The President said he would spend yesterday working with "key congressmen" on amendments to the proposal.He said he expected Congress to approve the bill by Tuesday.

"But that's just a temporary thing," he added. "We will work as hard as possible in the next few weeks to evolve for our country a permanent, long-range, comprehensive energy policy.

"We're the only developed nation in the world that doesn't have such a policy. And it's a very serious handicap to me and to the other leaders who are now dealing with this first indication of a permanent energy shortage."

Carter said the administration, under the guidance of energy chief James R. Schlesinger, will have a permanent energy plan by April 20.

In Pittsburgh the President said an amendment to the temporary measure could include a request to give the administration or states the authority to close the manufacturers of seasonal products in times of crisis.

"We have plants that use natural gas as a raw material and whose products are used primarily in the summertime," he said. "It might very well be that we could close down those plants on a two-week basis, or even for one month, and allot that fuel to companies that have to stay open on a continuing production basis."

However, Carter quickly added, "I wouldn't want to disrupt the normal free-enterprise system of allotting fuel and have the government take over the whole responsibility."

Carter also said he would "like very much for private industrial leaders, on an individual or plant basis, and mayors and governors, on a community or state basis, to consider shifting" to the four-day work week.

Carter said Saturday that he was thinking of asking Congress to legislate a temporary four-day work week to help deal with the fuel crisis. But yesterday in Pittsburgh he explained that it was only a thought.

"That's something that I cannot do now through the federal government because of legal prohibitions," he said. "But that's the kind of thing that ought to be available to us (the administration) as an option in the future."

The union officials, politicians and laid-off workers who gathered around Carter in the Westinghouse plant seemed to appreciate his visit. Carter apparently read the mood and mixed a tale of personal woe with his calls for sacrifice.

"The White House is cold inside," he said. "My wife, when I told her that we were going to turn down the thermostats drastically in the White House, she shed a few tears because she's "a really cold-natured person," he said lightheartedly.

"She had just gotten through with the inauguration ceremonies and a two-year campaign, and we had receptions in the White House to meet thousands of people and she was tired. When I told her (about lowering the temperature), she said: 'I just can't do it.' But we've gotten accustomed to it, and I hope that all of the people in the country will realize that we're all in it together."