President Carter asked the American people last night for "your support and understanding" as Congress nears its climactic votes on his national energy plan that would dramatically increase the price of energy to all consumers.

In a somber, nationally televised address from the White House, the President reiterated his arguments for his energy proposals, made last April, and declared that in the coming energy debates in House-Senate conference committees "the strength and courage of our political system will be proved."

Carter's appeal was exceptionally conciliatory, containing none of the harsh rhetaric he has used in the past. Nor did the speech advance any major new arguments for enactment of the administration energy plan, which the President has made his top domestic priority.

The price of energy, Carter warned, is going to continue to rise no matter what. The question before Congress, he said, is who will benefit from higher prices, the energy industry or the nation as a whole. His plan, the President said, would return that money to the public to stimulate the economy and create new jobs.

"The choices facing the members of Congress are not easy," he said. "For them to pass an effective and fair plan, they will need your support and understanding - your support to resist pressures from a few for special favors at the expense of the rest of us, and your understanding that there can be no effective plan without some sacrifices from all of us."

The tone of the speech was moderate, its rhetorical flourishes few. The President criticized "some of the oil companies" for seeking to profit from the energy legislation, but there was no talk of "rip-offs" or "potential war profiteering" by the oil industry as in the past.

Carter clearly hoped in the speech to mobilize various segments of the public behind his energy plan before the votes, later this month and stretching into December, in the conference committees. At issue in Congress is the House-passed version of the legislation, which contained most of what the President proposed last spring, and the Senate-passed version, where the major administration provisions were either killed or severely watered down.

But there was nothing in the speech to suggest anger or disappointment at what the Senate did to his original proposal.

"This is not a contest of strength between the President and the Congress, nor between the House and the Senate," Carter said."What is being measured is the strength and will of our nation - whether we can acknowledge a threat and meet a serious challenge together."

The President also sought to explain some of the reasons for the energy problem, speaking much like the father of a once-affluent family come upon hard times, explaining to the children why the amenities of life will be fewer and less lavish than in the past.

"We must face an unpleasant face about energy prices," he said. "They are going up, whether we pass an energy program or not, as fuel becomes scarcer and more expensive to produce."

This was the President's second television address to the nation on energy and like the first, made in April before he unveiled his proposals in a speech to Congress, its main thrust was the dangers the energy problem poses to the American economy. American lifestyles and even the security of the nation.

Seeking to dramatize how energy affects all segments of the populace he is seeking to mobilize, Carter said the cost of importing foreign oil in one year wipes out the value of two years worth of U.S. agricultural exports. Moreover, he said, imported oil causes unemployment, makes it harder to balance the federal budget, and feeds inflation.

"If this trend continues," Carter warned, the excessive reliance on foreign oil could make the very security of our nation increasingly dependent on uncertain energy suppliers. Our national security depends on more than our armed forces. It also rests on the strength of our economy, on our national will, and on the ability of the United States to carry out our foreign policy as a free and independent nation.

"America overseas is only as strong as America at home."

The President spoke from the Oval Office. A few feet away, in the Roosevelt Room of the White House, about 20 congressional leaders and members of the conference committees watched him on television sets. Carter met with the congressional delegation after his speech.

During the speech, the President made one reference to his decision, officially announced Monday, to postpone his planned trip to nine countries later this month so he can remain in Washington to lobby for the energy legislation. He said he has "no doubt that this is the right decision" because other nations of the world are awaiting the outcome of the energy battle in the United States.

Another factor in the postponement, not mentioned last night, was the White House fear of the domestic political repercussions for Carter should Congress dismember his energy plan while he was thousands of miles from home.

Stressing themes that are now familiar, the President said the United States' largest energy problem is the amount it wastes. He said it is important to "promote new oil and gas discoveries," which is what the oil industry seeks, but reiterated his assertion that his plan "would provide adequate incentives" to do that.

His original energy proposal, Carter said, has "three basic elements." He said these were fairness both to consumers and energy producers, provisions to promote conservation and increased production of oil and gas while gradually shifting to more plentiful energy sources, and protection against "any unreasonable financial burden" on the federal budget.

"These are the three standards by which the final legislation will be judged," he said. "I will sign the energy bills only if they meet these three tests."

The President concluded his address with an appeal for understanding and help and a warning about the consequences of failure.

"I said six months ago that no one would be completely satisfied with this national energy plan," he said. "That prediction has turned out to be right. There is some part of this complex legislation to which every region and every interest group can object.

"But a common national sacrifice to meet this serioud problem should be shared by everyone - a proof that the plan is fair. Many groups have risen to the challenge, but unfortunately there are still some who seek personal gain over the national interest."

Carter added, "All of us in government need your help."

Failure to act on the problem now, the President said, will mean that "we will surely face a greater series of crises tomorrow - energy shortages, environmental damage, ever more massive government bureaucracy and regulations, ill-considered crash programs."